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 $89.77   7.828%   $96.7972   $96.80   $96.80   $96.80  
  Purchase #2 $156.82   8.620%   $170.3379   $170.34   $170.35   $170.30  
  Purchase #3 $26.82   8.120%   $28.9978   $29.00   $29.00   $29.00  
  Purchase #4 $179.54   11.109%   $199.4851   $199.49   $199.50   $199.50  
  Purchase #5 $161.72   4.562%   $169.0977   $169.10   $169.10   $169.10  
  Purchase #6 $38.95   7.324%   $41.8027   $41.80   $41.80   $41.80  
  Purchase #7 $121.43   11.335%   $135.1941   $135.19   $135.20   $135.20  
  7 purchase totals = $775.05       $841.7125   $841.72   $841.75   $841.70