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 $112.87   11.292%   $125.6153   $125.62   $125.60   $125.60  
  Purchase #2 $118.95   4.509%   $124.3135   $124.31   $124.30   $124.30  
  Purchase #3 $223.71   6.538%   $238.3362   $238.34   $238.35   $238.30  
  Purchase #4 $44.51   10.692%   $49.269   $49.27   $49.25   $49.30  
  Purchase #5 $65.35   6.214%   $69.4108   $69.41   $69.40   $69.40  
  Purchase #6 $188.40   5.764%   $199.2594   $199.26   $199.25   $199.30  
  Purchase #7 $108.71   4.501%   $113.603   $113.60   $113.60   $113.60  
  7 purchase totals = $862.50       $919.8072   $919.81   $919.75   $919.80