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 $182.68   12.543%   $205.5936   $205.59   $205.60   $205.60  
  Purchase #2 $29.40   7.290%   $31.5433   $31.54   $31.55   $31.50  
  Purchase #3 $117.44   10.479%   $129.7465   $129.75   $129.75   $129.70  
  Purchase #4 $86.30   8.403%   $93.5518   $93.55   $93.55   $93.60  
  Purchase #5 $106.35   11.417%   $118.492   $118.49   $118.50   $118.50  
  Purchase #6 $185.59   5.323%   $195.469   $195.47   $195.45   $195.50  
  Purchase #7 $200.35   9.105%   $218.5919   $218.59   $218.60   $218.60  
  7 purchase totals = $908.11       $992.9881   $992.98   $993.00   $993.00