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 $106.87   9.241%   $116.7459   $116.75   $116.75   $116.70  
  Purchase #2 $68.87   3.523%   $71.2963   $71.30   $71.30   $71.30  
  Purchase #3 $44.62   10.825%   $49.4501   $49.45   $49.45   $49.50  
  Purchase #4 $104.32   3.541%   $108.014   $108.01   $108.00   $108.00  
  Purchase #5 $154.47   6.118%   $163.9205   $163.92   $163.90   $163.90  
  Purchase #6 $10.46   5.375%   $11.0222   $11.02   $11.00   $11.00  
  Purchase #7 $208.42   3.281%   $215.2583   $215.26   $215.25   $215.30  
  7 purchase totals = $698.03       $735.7073   $735.71   $735.65   $735.70