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 $176.44   5.657%   $186.4212   $186.42   $186.40   $186.40  
  Purchase #2 $93.42   8.658%   $101.5083   $101.51   $101.50   $101.50  
  Purchase #3 $188.37   3.374%   $194.7256   $194.73   $194.75   $194.70  
  Purchase #4 $205.43   5.763%   $217.2689   $217.27   $217.25   $217.30  
  Purchase #5 $152.96   10.811%   $169.4965   $169.50   $169.50   $169.50  
  Purchase #6 $43.49   6.225%   $46.1973   $46.20   $46.20   $46.20  
  Purchase #7 $81.96   8.231%   $88.7061   $88.71   $88.70   $88.70  
  7 purchase totals = $942.07       $1,004.3239   $1,004.34   $1,004.30   $1,004.30