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 $179.46   12.726%   $202.2981   $202.30   $202.30   $202.30  
  Purchase #2 $119.46   13.114%   $135.126   $135.13   $135.15   $135.10  
  Purchase #3 $37.29   13.180%   $42.2048   $42.20   $42.20   $42.20  
  Purchase #4 $244.78   11.601%   $273.1769   $273.18   $273.20   $273.20  
  Purchase #5 $234.59   6.178%   $249.083   $249.08   $249.10   $249.10  
  Purchase #6 $70.42   11.677%   $78.6429   $78.64   $78.65   $78.60  
  Purchase #7 $246.96   11.685%   $275.8173   $275.82   $275.80   $275.80  
  7 purchase totals = $1,132.96       $1,256.3490   $1,256.35   $1,256.40   $1,256.30