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 $247.87   5.628%   $261.8201   $261.82   $261.80   $261.80  
  Purchase #2 $243.41   11.490%   $271.3778   $271.38   $271.40   $271.40  
  Purchase #3 $139.72   10.431%   $154.2942   $154.29   $154.30   $154.30  
  Purchase #4 $57.71   7.302%   $61.924   $61.92   $61.90   $61.90  
  Purchase #5 $76.79   5.872%   $81.2991   $81.30   $81.30   $81.30  
  Purchase #6 $85.27   10.251%   $94.011   $94.01   $94.00   $94.00  
  Purchase #7 $121.79   11.551%   $135.858   $135.86   $135.85   $135.90  
  7 purchase totals = $972.56       $1,060.5842   $1,060.58   $1,060.55   $1,060.60