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 $188.29   9.852%   $206.8403   $206.84   $206.85   $206.80  
  Purchase #2 $72.69   6.124%   $77.1415   $77.14   $77.15   $77.10  
  Purchase #3 $157.26   6.809%   $167.9678   $167.97   $167.95   $168.00  
  Purchase #4 $46.96   12.653%   $52.9018   $52.90   $52.90   $52.90  
  Purchase #5 $181.66   10.781%   $201.2448   $201.24   $201.25   $201.20  
  Purchase #6 $121.85   8.218%   $131.8636   $131.86   $131.85   $131.90  
  Purchase #7 $153.87   10.725%   $170.3726   $170.37   $170.35   $170.40  
  7 purchase totals = $922.58       $1,008.3324   $1,008.32   $1,008.30   $1,008.30