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 $55.76   7.851%   $60.1377   $60.14   $60.15   $60.10  
  Purchase #2 $197.58   9.538%   $216.4252   $216.43   $216.45   $216.40  
  Purchase #3 $169.67   10.114%   $186.8304   $186.83   $186.85   $186.80  
  Purchase #4 $155.35   9.677%   $170.3832   $170.38   $170.40   $170.40  
  Purchase #5 $24.98   11.413%   $27.831   $27.83   $27.85   $27.80  
  Purchase #6 $219.85   12.428%   $247.173   $247.17   $247.15   $247.20  
  Purchase #7 $76.74   12.704%   $86.489   $86.49   $86.50   $86.50  
  7 purchase totals = $899.93       $995.2695   $995.27   $995.35   $995.20