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 $46.30   13.408%   $52.5079   $52.51   $52.50   $52.50  
  Purchase #2 $227.45   10.132%   $250.4952   $250.50   $250.50   $250.50  
  Purchase #3 $76.59   9.180%   $83.621   $83.62   $83.60   $83.60  
  Purchase #4 $128.52   3.298%   $132.7586   $132.76   $132.75   $132.80  
  Purchase #5 $64.52   7.726%   $69.5048   $69.50   $69.50   $69.50  
  Purchase #6 $112.76   10.106%   $124.1555   $124.16   $124.15   $124.20  
  Purchase #7 $152.34   5.847%   $161.2473   $161.25   $161.25   $161.20  
  7 purchase totals = $808.48       $874.2903   $874.30   $874.25   $874.30