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 $91.60   13.633%   $104.0878   $104.09   $104.10   $104.10  
  Purchase #2 $125.27   6.634%   $133.5804   $133.58   $133.60   $133.60  
  Purchase #3 $61.71   11.646%   $68.8967   $68.90   $68.90   $68.90  
  Purchase #4 $163.63   11.449%   $182.364   $182.36   $182.35   $182.40  
  Purchase #5 $11.25   12.745%   $12.6838   $12.68   $12.70   $12.70  
  Purchase #6 $170.76   10.579%   $188.8247   $188.82   $188.80   $188.80  
  Purchase #7 $140.70   3.366%   $145.436   $145.44   $145.45   $145.40  
  7 purchase totals = $764.92       $835.8734   $835.87   $835.90   $835.90