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 $136.32   12.201%   $152.9524   $152.95   $152.95   $153.00  
  Purchase #2 $93.74   10.837%   $103.8986   $103.90   $103.90   $103.90  
  Purchase #3 $112.93   10.639%   $124.9446   $124.94   $124.95   $124.90  
  Purchase #4 $133.67   9.722%   $146.6654   $146.67   $146.65   $146.70  
  Purchase #5 $68.69   8.765%   $74.7107   $74.71   $74.70   $74.70  
  Purchase #6 $162.94   12.487%   $183.2863   $183.29   $183.30   $183.30  
  Purchase #7 $163.40   13.287%   $185.111   $185.11   $185.10   $185.10  
  7 purchase totals = $871.69       $971.5690   $971.57   $971.55   $971.60