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 $148.91   7.522%   $160.111   $160.11   $160.10   $160.10  
  Purchase #2 $105.82   8.543%   $114.8602   $114.86   $114.85   $114.90  
  Purchase #3 $32.77   5.851%   $34.6874   $34.69   $34.70   $34.70  
  Purchase #4 $106.45   5.873%   $112.7018   $112.70   $112.70   $112.70  
  Purchase #5 $86.86   12.152%   $97.4152   $97.42   $97.40   $97.40  
  Purchase #6 $197.50   9.262%   $215.7925   $215.79   $215.80   $215.80  
  Purchase #7 $116.92   11.562%   $130.4383   $130.44   $130.45   $130.40  
  7 purchase totals = $795.23       $866.0064   $866.01   $866.00   $866.00