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 $222.54   8.421%   $241.2801   $241.28   $241.30   $241.30  
  Purchase #2 $51.72   13.642%   $58.7756   $58.78   $58.80   $58.80  
  Purchase #3 $144.34   11.852%   $161.4472   $161.45   $161.45   $161.40  
  Purchase #4 $94.67   8.872%   $103.0691   $103.07   $103.05   $103.10  
  Purchase #5 $76.48   3.549%   $79.1943   $79.19   $79.20   $79.20  
  Purchase #6 $100.78   8.582%   $109.4289   $109.43   $109.45   $109.40  
  Purchase #7 $11.39   3.178%   $11.752   $11.75   $11.75   $11.80  
  7 purchase totals = $701.92       $764.9472   $764.95   $765.00   $765.00