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 $186.95   13.567%   $212.3135   $212.31   $212.30   $212.30  
  Purchase #2 $30.45   10.689%   $33.7048   $33.70   $33.70   $33.70  
  Purchase #3 $168.71   8.562%   $183.155   $183.16   $183.15   $183.20  
  Purchase #4 $28.39   13.370%   $32.1857   $32.19   $32.20   $32.20  
  Purchase #5 $133.96   13.671%   $152.2737   $152.27   $152.25   $152.30  
  Purchase #6 $94.90   13.211%   $107.4372   $107.44   $107.45   $107.40  
  Purchase #7 $67.86   10.138%   $74.7396   $74.74   $74.75   $74.70  
  7 purchase totals = $711.22       $795.8095   $795.81   $795.80   $795.80