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 $105.65   12.404%   $118.7548   $118.75   $118.75   $118.80  
  Purchase #2 $65.63   11.107%   $72.9195   $72.92   $72.90   $72.90  
  Purchase #3 $249.91   3.836%   $259.4965   $259.50   $259.50   $259.50  
  Purchase #4 $10.25   12.471%   $11.5283   $11.53   $11.55   $11.50  
  Purchase #5 $187.56   8.360%   $203.24   $203.24   $203.25   $203.20  
  Purchase #6 $100.78   3.663%   $104.4716   $104.47   $104.45   $104.50  
  Purchase #7 $70.54   7.497%   $75.8284   $75.83   $75.85   $75.80  
  7 purchase totals = $790.32       $846.2391   $846.24   $846.25   $846.20