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 $68.34   11.763%   $76.3788   $76.38   $76.40   $76.40  
  Purchase #2 $250.62   12.228%   $281.2658   $281.27   $281.25   $281.30  
  Purchase #3 $113.27   9.565%   $124.1043   $124.10   $124.10   $124.10  
  Purchase #4 $165.82   13.573%   $188.3267   $188.33   $188.35   $188.30  
  Purchase #5 $26.67   13.508%   $30.2726   $30.27   $30.25   $30.30  
  Purchase #6 $77.36   6.301%   $82.2345   $82.23   $82.25   $82.20  
  Purchase #7 $149.94   9.231%   $163.781   $163.78   $163.80   $163.80  
  7 purchase totals = $852.02       $946.3637   $946.36   $946.40   $946.40