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 $88.65   5.389%   $93.4273   $93.43   $93.45   $93.40  
  Purchase #2 $201.64   4.718%   $211.1534   $211.15   $211.15   $211.20  
  Purchase #3 $76.68   10.590%   $84.8004   $84.80   $84.80   $84.80  
  Purchase #4 $143.25   3.317%   $148.0016   $148.00   $148.00   $148.00  
  Purchase #5 $197.86   8.871%   $215.4122   $215.41   $215.40   $215.40  
  Purchase #6 $244.50   4.671%   $255.9206   $255.92   $255.90   $255.90  
  Purchase #7 $44.72   5.445%   $47.155   $47.16   $47.15   $47.20  
  7 purchase totals = $997.30       $1,055.8705   $1,055.87   $1,055.85   $1,055.90