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 $30.40   5.525%   $32.0796   $32.08   $32.10   $32.10  
  Purchase #2 $19.78   11.622%   $22.0788   $22.08   $22.10   $22.10  
  Purchase #3 $68.31   12.865%   $77.0981   $77.10   $77.10   $77.10  
  Purchase #4 $201.38   7.190%   $215.8592   $215.86   $215.85   $215.90  
  Purchase #5 $177.25   12.334%   $199.112   $199.11   $199.10   $199.10  
  Purchase #6 $142.48   13.212%   $161.3045   $161.30   $161.30   $161.30  
  Purchase #7 $101.27   4.781%   $106.1117   $106.11   $106.10   $106.10  
  7 purchase totals = $740.87       $813.6439   $813.64   $813.65   $813.70