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 $119.74   4.393%   $125.0002   $125.00   $125.00   $125.00  
  Purchase #2 $114.67   8.363%   $124.2599   $124.26   $124.25   $124.30  
  Purchase #3 $14.51   6.851%   $15.5041   $15.50   $15.50   $15.50  
  Purchase #4 $197.89   9.343%   $216.3789   $216.38   $216.40   $216.40  
  Purchase #5 $157.94   11.236%   $175.6861   $175.69   $175.70   $175.70  
  Purchase #6 $64.73   11.112%   $71.9228   $71.92   $71.90   $71.90  
  Purchase #7 $143.71   8.489%   $155.9095   $155.91   $155.90   $155.90  
  7 purchase totals = $813.19       $884.6615   $884.66   $884.65   $884.70