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 $60.51   4.826%   $63.4302   $63.43   $63.45   $63.40  
  Purchase #2 $124.27   6.186%   $131.9573   $131.96   $131.95   $132.00  
  Purchase #3 $199.70   10.811%   $221.2896   $221.29   $221.30   $221.30  
  Purchase #4 $203.42   10.752%   $225.2917   $225.29   $225.30   $225.30  
  Purchase #5 $96.78   9.845%   $106.308   $106.31   $106.30   $106.30  
  Purchase #6 $126.78   8.175%   $137.1443   $137.14   $137.15   $137.10  
  Purchase #7 $81.93   4.540%   $85.6496   $85.65   $85.65   $85.60  
  7 purchase totals = $893.39       $971.0707   $971.07   $971.10   $971.00