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 $215.68   13.179%   $244.1045   $244.10   $244.10   $244.10  
  Purchase #2 $187.63   3.637%   $194.4541   $194.45   $194.45   $194.50  
  Purchase #3 $248.94   9.462%   $272.4947   $272.49   $272.50   $272.50  
  Purchase #4 $234.75   13.597%   $266.669   $266.67   $266.65   $266.70  
  Purchase #5 $207.64   13.688%   $236.0618   $236.06   $236.05   $236.10  
  Purchase #6 $108.82   8.304%   $117.8564   $117.86   $117.85   $117.90  
  Purchase #7 $72.89   11.183%   $81.0413   $81.04   $81.05   $81.00  
  7 purchase totals = $1,276.35       $1,412.6818   $1,412.67   $1,412.65   $1,412.80