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 $46.91   6.552%   $49.9835   $49.98   $50.00   $50.00  
  Purchase #2 $200.33   3.392%   $207.1252   $207.13   $207.15   $207.10  
  Purchase #3 $43.32   5.660%   $45.7719   $45.77   $45.75   $45.80  
  Purchase #4 $193.98   10.129%   $213.6282   $213.63   $213.65   $213.60  
  Purchase #5 $245.86   3.762%   $255.1093   $255.11   $255.10   $255.10  
  Purchase #6 $154.66   5.523%   $163.2019   $163.20   $163.20   $163.20  
  Purchase #7 $236.67   12.516%   $266.2916   $266.29   $266.30   $266.30  
  7 purchase totals = $1,121.73       $1,201.1116   $1,201.11   $1,201.15   $1,201.10