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 $232.48   12.318%   $261.1169   $261.12   $261.10   $261.10  
  Purchase #2 $237.96   6.562%   $253.5749   $253.57   $253.55   $253.60  
  Purchase #3 $40.61   3.821%   $42.1617   $42.16   $42.15   $42.20  
  Purchase #4 $157.70   4.802%   $165.2728   $165.27   $165.25   $165.30  
  Purchase #5 $247.55   9.489%   $271.04   $271.04   $271.05   $271.00  
  Purchase #6 $112.93   5.443%   $119.0768   $119.08   $119.10   $119.10  
  Purchase #7 $248.92   11.442%   $277.4014   $277.40   $277.40   $277.40  
  7 purchase totals = $1,278.15       $1,389.6445   $1,389.64   $1,389.60   $1,389.70