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 $240.92   6.608%   $256.84   $256.84   $256.85   $256.80  
  Purchase #2 $103.75   3.581%   $107.4653   $107.47   $107.45   $107.50  
  Purchase #3 $210.33   12.181%   $235.9503   $235.95   $235.95   $236.00  
  Purchase #4 $199.26   9.548%   $218.2853   $218.29   $218.30   $218.30  
  Purchase #5 $245.52   6.465%   $261.3929   $261.39   $261.40   $261.40  
  Purchase #6 $127.66   6.112%   $135.4626   $135.46   $135.45   $135.50  
  Purchase #7 $234.44   9.305%   $256.2546   $256.25   $256.25   $256.30  
  7 purchase totals = $1,361.88       $1,471.6510   $1,471.65   $1,471.65   $1,471.80