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 $250.67   12.870%   $282.9312   $282.93   $282.95   $282.90  
  Purchase #2 $54.98   11.375%   $61.234   $61.23   $61.25   $61.20  
  Purchase #3 $28.77   11.257%   $32.0086   $32.01   $32.00   $32.00  
  Purchase #4 $79.88   10.439%   $88.2187   $88.22   $88.20   $88.20  
  Purchase #5 $64.87   3.438%   $67.1002   $67.10   $67.10   $67.10  
  Purchase #6 $141.62   13.169%   $160.2699   $160.27   $160.25   $160.30  
  Purchase #7 $176.83   4.175%   $184.2127   $184.21   $184.20   $184.20  
  7 purchase totals = $797.62       $875.9753   $875.97   $875.95   $875.90