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 $84.88   11.267%   $94.4434   $94.44   $94.45   $94.40  
  Purchase #2 $163.66   13.435%   $185.6477   $185.65   $185.65   $185.60  
  Purchase #3 $152.63   9.408%   $166.9894   $166.99   $167.00   $167.00  
  Purchase #4 $78.40   6.663%   $83.6238   $83.62   $83.60   $83.60  
  Purchase #5 $9.43   5.314%   $9.9311   $9.93   $9.95   $9.90  
  Purchase #6 $152.92   5.462%   $161.2725   $161.27   $161.25   $161.30  
  Purchase #7 $16.92   7.601%   $18.2061   $18.21   $18.20   $18.20  
  7 purchase totals = $658.84       $720.1140   $720.11   $720.10   $720.00