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 $50.46   5.792%   $53.3826   $53.38   $53.40   $53.40  
  Purchase #2 $167.85   7.150%   $179.8513   $179.85   $179.85   $179.90  
  Purchase #3 $234.37   6.541%   $249.7001   $249.70   $249.70   $249.70  
  Purchase #4 $169.52   7.805%   $182.751   $182.75   $182.75   $182.80  
  Purchase #5 $151.96   7.604%   $163.515   $163.52   $163.50   $163.50  
  Purchase #6 $107.33   11.669%   $119.8543   $119.85   $119.85   $119.90  
  Purchase #7 $5.54   5.235%   $5.83   $5.83   $5.85   $5.80  
  7 purchase totals = $887.03       $954.8843   $954.88   $954.90   $955.00