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 $37.75   9.535%   $41.3495   $41.35   $41.35   $41.30  
  Purchase #2 $176.65   10.687%   $195.5286   $195.53   $195.55   $195.50  
  Purchase #3 $247.52   11.495%   $275.9724   $275.97   $275.95   $276.00  
  Purchase #4 $187.93   5.535%   $198.3319   $198.33   $198.35   $198.30  
  Purchase #5 $100.66   11.335%   $112.0698   $112.07   $112.05   $112.10  
  Purchase #6 $242.44   11.197%   $269.586   $269.59   $269.60   $269.60  
  Purchase #7 $111.27   13.224%   $125.9843   $125.98   $126.00   $126.00  
  7 purchase totals = $1,104.22       $1,218.8225   $1,218.82   $1,218.85   $1,218.80