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 $100.45   7.630%   $108.1143   $108.11   $108.10   $108.10  
  Purchase #2 $81.94   11.800%   $91.6089   $91.61   $91.60   $91.60  
  Purchase #3 $29.86   3.218%   $30.8209   $30.82   $30.80   $30.80  
  Purchase #4 $147.89   8.379%   $160.2817   $160.28   $160.30   $160.30  
  Purchase #5 $139.99   12.219%   $157.0954   $157.10   $157.10   $157.10  
  Purchase #6 $11.91   11.728%   $13.3068   $13.31   $13.30   $13.30  
  Purchase #7 $88.88   4.484%   $92.8654   $92.87   $92.85   $92.90  
  7 purchase totals = $600.92       $654.0934   $654.10   $654.05   $654.10