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 $247.86   8.395%   $268.6678   $268.67   $268.65   $268.70  
  Purchase #2 $54.68   10.864%   $60.6204   $60.62   $60.60   $60.60  
  Purchase #3 $238.47   4.549%   $249.318   $249.32   $249.30   $249.30  
  Purchase #4 $23.42   4.506%   $24.4753   $24.48   $24.50   $24.50  
  Purchase #5 $232.52   12.665%   $261.9687   $261.97   $261.95   $262.00  
  Purchase #6 $148.77   11.250%   $165.5066   $165.51   $165.50   $165.50  
  Purchase #7 $69.72   5.784%   $73.7526   $73.75   $73.75   $73.80  
  7 purchase totals = $1,015.44       $1,104.3094   $1,104.32   $1,104.25   $1,104.40