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 $217.91   3.530%   $225.6022   $225.60   $225.60   $225.60  
  Purchase #2 $118.68   5.781%   $125.5409   $125.54   $125.55   $125.50  
  Purchase #3 $168.30   9.480%   $184.2548   $184.25   $184.25   $184.30  
  Purchase #4 $116.92   8.423%   $126.7682   $126.77   $126.75   $126.80  
  Purchase #5 $156.27   10.132%   $172.1033   $172.10   $172.10   $172.10  
  Purchase #6 $149.59   8.259%   $161.9446   $161.94   $161.95   $161.90  
  Purchase #7 $27.48   11.207%   $30.5597   $30.56   $30.55   $30.60  
  7 purchase totals = $955.15       $1,026.7737   $1,026.76   $1,026.75   $1,026.80