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 $60.27   10.808%   $66.784   $66.78   $66.80   $66.80  
  Purchase #2 $245.90   6.510%   $261.9081   $261.91   $261.90   $261.90  
  Purchase #3 $149.70   13.342%   $169.673   $169.67   $169.65   $169.70  
  Purchase #4 $121.82   3.626%   $126.2372   $126.24   $126.25   $126.20  
  Purchase #5 $250.30   13.774%   $284.7763   $284.78   $284.80   $284.80  
  Purchase #6 $62.42   4.574%   $65.2751   $65.28   $65.30   $65.30  
  Purchase #7 $165.97   6.318%   $176.456   $176.46   $176.45   $176.50  
  7 purchase totals = $1,056.38       $1,151.1097   $1,151.12   $1,151.15   $1,151.20