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 $54.44   4.376%   $56.8223   $56.82   $56.80   $56.80  
  Purchase #2 $244.72   13.350%   $277.3901   $277.39   $277.40   $277.40  
  Purchase #3 $64.85   4.863%   $68.0037   $68.00   $68.00   $68.00  
  Purchase #4 $46.75   10.181%   $51.5096   $51.51   $51.50   $51.50  
  Purchase #5 $132.55   12.203%   $148.7251   $148.73   $148.75   $148.70  
  Purchase #6 $249.93   7.760%   $269.3246   $269.32   $269.30   $269.30  
  Purchase #7 $167.63   10.162%   $184.6646   $184.66   $184.65   $184.70  
  7 purchase totals = $960.87       $1,056.4400   $1,056.43   $1,056.40   $1,056.40