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 $200.71   5.636%   $212.022   $212.02   $212.00   $212.00  
  Purchase #2 $30.38   11.819%   $33.9706   $33.97   $33.95   $34.00  
  Purchase #3 $87.84   6.422%   $93.4811   $93.48   $93.50   $93.50  
  Purchase #4 $67.66   13.348%   $76.6913   $76.69   $76.70   $76.70  
  Purchase #5 $52.89   3.604%   $54.7962   $54.80   $54.80   $54.80  
  Purchase #6 $124.85   5.562%   $131.7942   $131.79   $131.80   $131.80  
  Purchase #7 $209.91   9.659%   $230.1852   $230.19   $230.20   $230.20  
  7 purchase totals = $774.24       $832.9406   $832.94   $832.95   $833.00