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 $6.96   5.145%   $7.3181   $7.32   $7.30   $7.30  
  Purchase #2 $234.89   11.397%   $261.6604   $261.66   $261.65   $261.70  
  Purchase #3 $76.31   8.767%   $83.0001   $83.00   $83.00   $83.00  
  Purchase #4 $199.86   6.869%   $213.5884   $213.59   $213.60   $213.60  
  Purchase #5 $85.99   11.814%   $96.1489   $96.15   $96.15   $96.10  
  Purchase #6 $81.43   11.390%   $90.7049   $90.70   $90.70   $90.70  
  Purchase #7 $16.52   4.802%   $17.3133   $17.31   $17.30   $17.30  
  7 purchase totals = $701.96       $769.7341   $769.73   $769.70   $769.70