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 $210.76   11.266%   $234.5042   $234.50   $234.50   $234.50  
  Purchase #2 $145.94   8.779%   $158.7521   $158.75   $158.75   $158.80  
  Purchase #3 $155.26   9.257%   $169.6324   $169.63   $169.65   $169.60  
  Purchase #4 $191.88   7.495%   $206.2614   $206.26   $206.25   $206.30  
  Purchase #5 $230.76   10.379%   $254.7106   $254.71   $254.70   $254.70  
  Purchase #6 $205.90   12.348%   $231.3245   $231.32   $231.30   $231.30  
  Purchase #7 $105.87   12.837%   $119.4605   $119.46   $119.45   $119.50  
  7 purchase totals = $1,246.37       $1,374.6457   $1,374.63   $1,374.60   $1,374.70