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 $204.92   5.257%   $215.6926   $215.69   $215.70   $215.70  
  Purchase #2 $192.91   11.845%   $215.7602   $215.76   $215.75   $215.80  
  Purchase #3 $58.79   8.733%   $63.9241   $63.92   $63.90   $63.90  
  Purchase #4 $21.66   13.513%   $24.5869   $24.59   $24.60   $24.60  
  Purchase #5 $65.45   11.448%   $72.9427   $72.94   $72.95   $72.90  
  Purchase #6 $211.28   10.299%   $233.0397   $233.04   $233.05   $233.00  
  Purchase #7 $126.70   5.250%   $133.3518   $133.35   $133.35   $133.40  
  7 purchase totals = $881.71       $959.2980   $959.29   $959.30   $959.30