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 $68.60   7.255%   $73.5769   $73.58   $73.60   $73.60  
  Purchase #2 $194.66   11.317%   $216.6897   $216.69   $216.70   $216.70  
  Purchase #3 $148.61   8.788%   $161.6698   $161.67   $161.65   $161.70  
  Purchase #4 $212.72   6.798%   $227.1807   $227.18   $227.20   $227.20  
  Purchase #5 $180.33   11.733%   $201.4881   $201.49   $201.50   $201.50  
  Purchase #6 $121.74   13.698%   $138.4159   $138.42   $138.40   $138.40  
  Purchase #7 $234.82   6.831%   $250.8606   $250.86   $250.85   $250.90  
  7 purchase totals = $1,161.48       $1,269.8817   $1,269.89   $1,269.90   $1,270.00