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 $118.92   10.689%   $131.6314   $131.63   $131.65   $131.60  
  Purchase #2 $78.77   11.235%   $87.6198   $87.62   $87.60   $87.60  
  Purchase #3 $116.70   11.592%   $130.2279   $130.23   $130.25   $130.20  
  Purchase #4 $228.71   13.850%   $260.3863   $260.39   $260.40   $260.40  
  Purchase #5 $144.75   5.733%   $153.0485   $153.05   $153.05   $153.00  
  Purchase #6 $97.96   13.873%   $111.55   $111.55   $111.55   $111.60  
  Purchase #7 $189.25   6.619%   $201.7765   $201.78   $201.80   $201.80  
  7 purchase totals = $975.06       $1,076.2404   $1,076.25   $1,076.30   $1,076.20