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 $56.64   9.745%   $62.1596   $62.16   $62.15   $62.20  
  Purchase #2 $248.47   5.301%   $261.6414   $261.64   $261.65   $261.60  
  Purchase #3 $217.61   6.256%   $231.2237   $231.22   $231.20   $231.20  
  Purchase #4 $120.63   12.197%   $135.3432   $135.34   $135.35   $135.30  
  Purchase #5 $241.90   11.708%   $270.2217   $270.22   $270.20   $270.20  
  Purchase #6 $217.30   12.224%   $243.8628   $243.86   $243.85   $243.90  
  Purchase #7 $12.95   7.825%   $13.9633   $13.96   $13.95   $14.00  
  7 purchase totals = $1,115.50       $1,218.4157   $1,218.40   $1,218.35   $1,218.40