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 $119.38   13.694%   $135.7279   $135.73   $135.75   $135.70  
  Purchase #2 $168.47   10.794%   $186.6547   $186.65   $186.65   $186.70  
  Purchase #3 $22.35   8.830%   $24.3235   $24.32   $24.30   $24.30  
  Purchase #4 $202.31   4.262%   $210.9325   $210.93   $210.95   $210.90  
  Purchase #5 $24.73   8.245%   $26.769   $26.77   $26.75   $26.80  
  Purchase #6 $31.49   10.372%   $34.7561   $34.76   $34.75   $34.80  
  Purchase #7 $53.36   9.189%   $58.2633   $58.26   $58.25   $58.30  
  7 purchase totals = $622.09       $677.4270   $677.42   $677.40   $677.50