Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
  Case Tag  
Price  
Sales  
Tax %  
Raw Total  
Incl. Sales Tax  
Rounded  
to Penny  
Rounded  
to Nickel  
Rounded  
to Dime  
  Purchase #1 $110.93   6.851%   $118.5298   $118.53   $118.55   $118.50  
  Purchase #2 $203.97   13.234%   $230.9634   $230.96   $230.95   $231.00  
  Purchase #3 $135.34   9.792%   $148.5925   $148.59   $148.60   $148.60  
  Purchase #4 $125.98   9.798%   $138.3235   $138.32   $138.30   $138.30  
  Purchase #5 $149.64   13.164%   $169.3386   $169.34   $169.35   $169.30  
  Purchase #6 $123.26   6.419%   $131.1721   $131.17   $131.15   $131.20  
  Purchase #7 $243.70   11.532%   $271.8035   $271.80   $271.80   $271.80  
  7 purchase totals = $1,092.82       $1,208.7234   $1,208.71   $1,208.70   $1,208.70