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 $112.38   11.754%   $125.5891   $125.59   $125.60   $125.60  
  Purchase #2 $25.77   3.328%   $26.6276   $26.63   $26.65   $26.60  
  Purchase #3 $180.84   13.220%   $204.747   $204.75   $204.75   $204.70  
  Purchase #4 $250.46   5.413%   $264.0174   $264.02   $264.00   $264.00  
  Purchase #5 $204.57   12.313%   $229.7587   $229.76   $229.75   $229.80  
  Purchase #6 $106.25   5.287%   $111.8674   $111.87   $111.85   $111.90  
  Purchase #7 $69.96   12.147%   $78.458   $78.46   $78.45   $78.50  
  7 purchase totals = $950.23       $1,041.0652   $1,041.08   $1,041.05   $1,041.10