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 $176.85   13.855%   $201.3526   $201.35   $201.35   $201.40  
  Purchase #2 $48.39   3.210%   $49.9433   $49.94   $49.95   $49.90  
  Purchase #3 $219.48   11.428%   $244.5622   $244.56   $244.55   $244.60  
  Purchase #4 $178.86   13.193%   $202.457   $202.46   $202.45   $202.50  
  Purchase #5 $21.41   11.676%   $23.9098   $23.91   $23.90   $23.90  
  Purchase #6 $43.46   9.359%   $47.5274   $47.53   $47.55   $47.50  
  Purchase #7 $191.67   8.220%   $207.4253   $207.43   $207.45   $207.40  
  7 purchase totals = $880.12       $977.1776   $977.18   $977.20   $977.20