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 $84.54   8.736%   $91.9254   $91.93   $91.95   $91.90  
  Purchase #2 $199.45   13.503%   $226.3817   $226.38   $226.40   $226.40  
  Purchase #3 $67.71   3.610%   $70.1543   $70.15   $70.15   $70.20  
  Purchase #4 $183.92   9.870%   $202.0729   $202.07   $202.05   $202.10  
  Purchase #5 $126.38   3.364%   $130.6314   $130.63   $130.65   $130.60  
  Purchase #6 $56.31   5.606%   $59.4667   $59.47   $59.45   $59.50  
  Purchase #7 $171.63   4.801%   $179.87   $179.87   $179.85   $179.90  
  7 purchase totals = $889.94       $960.5024   $960.50   $960.50   $960.60