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 $231.34   12.513%   $260.2876   $260.29   $260.30   $260.30  
  Purchase #2 $220.71   13.848%   $251.2739   $251.27   $251.25   $251.30  
  Purchase #3 $168.82   4.663%   $176.6921   $176.69   $176.70   $176.70  
  Purchase #4 $245.95   4.591%   $257.2416   $257.24   $257.25   $257.20  
  Purchase #5 $193.94   3.738%   $201.1895   $201.19   $201.20   $201.20  
  Purchase #6 $185.54   13.633%   $210.8347   $210.83   $210.85   $210.80  
  Purchase #7 $51.93   5.220%   $54.6407   $54.64   $54.65   $54.60  
  7 purchase totals = $1,298.23       $1,412.1601   $1,412.15   $1,412.20   $1,412.10