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 $185.49   8.701%   $201.6295   $201.63   $201.65   $201.60  
  Purchase #2 $86.34   8.465%   $93.6487   $93.65   $93.65   $93.60  
  Purchase #3 $220.31   8.568%   $239.1862   $239.19   $239.20   $239.20  
  Purchase #4 $47.65   12.166%   $53.4471   $53.45   $53.45   $53.40  
  Purchase #5 $93.79   13.243%   $106.2106   $106.21   $106.20   $106.20  
  Purchase #6 $58.35   12.648%   $65.7301   $65.73   $65.75   $65.70  
  Purchase #7 $247.47   12.733%   $278.9804   $278.98   $279.00   $279.00  
  7 purchase totals = $939.40       $1,038.8326   $1,038.84   $1,038.90   $1,038.70