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 $106.96   5.213%   $112.5358   $112.54   $112.55   $112.50  
  Purchase #2 $58.28   9.554%   $63.8481   $63.85   $63.85   $63.80  
  Purchase #3 $244.32   4.644%   $255.6662   $255.67   $255.65   $255.70  
  Purchase #4 $78.44   11.817%   $87.7093   $87.71   $87.70   $87.70  
  Purchase #5 $148.44   7.627%   $159.7615   $159.76   $159.75   $159.80  
  Purchase #6 $9.85   3.430%   $10.1879   $10.19   $10.20   $10.20  
  Purchase #7 $114.88   5.723%   $121.4546   $121.45   $121.45   $121.50  
  7 purchase totals = $761.17       $811.1634   $811.17   $811.15   $811.20