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 $121.38   3.786%   $125.9754   $125.98   $126.00   $126.00  
  Purchase #2 $54.28   11.451%   $60.4956   $60.50   $60.50   $60.50  
  Purchase #3 $71.61   13.324%   $81.1513   $81.15   $81.15   $81.20  
  Purchase #4 $191.79   10.596%   $212.1121   $212.11   $212.10   $212.10  
  Purchase #5 $92.88   10.327%   $102.4717   $102.47   $102.45   $102.50  
  Purchase #6 $110.56   9.107%   $120.6287   $120.63   $120.65   $120.60  
  Purchase #7 $205.41   5.781%   $217.2848   $217.28   $217.30   $217.30  
  7 purchase totals = $847.91       $920.1196   $920.12   $920.15   $920.20