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 $125.73   8.126%   $135.9468   $135.95   $135.95   $135.90  
  Purchase #2 $66.69   12.116%   $74.7702   $74.77   $74.75   $74.80  
  Purchase #3 $22.75   10.512%   $25.1415   $25.14   $25.15   $25.10  
  Purchase #4 $56.49   11.505%   $62.9892   $62.99   $63.00   $63.00  
  Purchase #5 $53.26   11.607%   $59.4419   $59.44   $59.45   $59.40  
  Purchase #6 $193.32   5.319%   $203.6027   $203.60   $203.60   $203.60  
  Purchase #7 $181.75   13.232%   $205.7992   $205.80   $205.80   $205.80  
  7 purchase totals = $699.99       $767.6915   $767.69   $767.70   $767.60