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 $146.28   8.494%   $158.705   $158.71   $158.70   $158.70  
  Purchase #2 $144.82   4.181%   $150.8749   $150.87   $150.85   $150.90  
  Purchase #3 $23.54   8.526%   $25.547   $25.55   $25.55   $25.50  
  Purchase #4 $211.49   11.615%   $236.0546   $236.05   $236.05   $236.10  
  Purchase #5 $113.65   3.732%   $117.8914   $117.89   $117.90   $117.90  
  Purchase #6 $196.55   9.163%   $214.5599   $214.56   $214.55   $214.60  
  Purchase #7 $22.82   3.694%   $23.663   $23.66   $23.65   $23.70  
  7 purchase totals = $859.15       $927.2958   $927.29   $927.25   $927.40