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 $218.29   3.149%   $225.164   $225.16   $225.15   $225.20  
  Purchase #2 $18.89   12.861%   $21.3194   $21.32   $21.30   $21.30  
  Purchase #3 $72.38   4.317%   $75.5046   $75.50   $75.50   $75.50  
  Purchase #4 $91.46   7.424%   $98.25   $98.25   $98.25   $98.30  
  Purchase #5 $158.50   11.130%   $176.1411   $176.14   $176.15   $176.10  
  Purchase #6 $204.26   3.799%   $212.0198   $212.02   $212.00   $212.00  
  Purchase #7 $187.67   10.510%   $207.3941   $207.39   $207.40   $207.40  
  7 purchase totals = $951.45       $1,015.7930   $1,015.78   $1,015.75   $1,015.80