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 $236.75   11.822%   $264.7386   $264.74   $264.75   $264.70  
  Purchase #2 $14.73   3.589%   $15.2587   $15.26   $15.25   $15.30  
  Purchase #3 $61.97   10.540%   $68.5016   $68.50   $68.50   $68.50  
  Purchase #4 $64.93   13.417%   $73.6417   $73.64   $73.65   $73.60  
  Purchase #5 $213.41   7.401%   $229.2045   $229.20   $229.20   $229.20  
  Purchase #6 $14.84   8.476%   $16.0978   $16.10   $16.10   $16.10  
  Purchase #7 $119.74   4.686%   $125.351   $125.35   $125.35   $125.40  
  7 purchase totals = $726.37       $792.7939   $792.79   $792.80   $792.80