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 $47.61   13.178%   $53.884   $53.88   $53.90   $53.90  
  Purchase #2 $58.97   4.416%   $61.5741   $61.57   $61.55   $61.60  
  Purchase #3 $213.29   10.297%   $235.2525   $235.25   $235.25   $235.30  
  Purchase #4 $233.71   11.442%   $260.4511   $260.45   $260.45   $260.50  
  Purchase #5 $164.93   3.219%   $170.2391   $170.24   $170.25   $170.20  
  Purchase #6 $48.86   12.128%   $54.7857   $54.79   $54.80   $54.80  
  Purchase #7 $14.42   8.474%   $15.642   $15.64   $15.65   $15.60  
  7 purchase totals = $781.79       $851.8285   $851.82   $851.85   $851.90