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 $126.49   6.331%   $134.4981   $134.50   $134.50   $134.50  
  Purchase #2 $139.42   10.287%   $153.7621   $153.76   $153.75   $153.80  
  Purchase #3 $89.62   4.544%   $93.6923   $93.69   $93.70   $93.70  
  Purchase #4 $101.38   11.514%   $113.0529   $113.05   $113.05   $113.10  
  Purchase #5 $202.32   6.276%   $215.0176   $215.02   $215.00   $215.00  
  Purchase #6 $150.38   5.287%   $158.3306   $158.33   $158.35   $158.30  
  Purchase #7 $156.76   11.112%   $174.1792   $174.18   $174.20   $174.20  
  7 purchase totals = $966.37       $1,042.5328   $1,042.53   $1,042.55   $1,042.60