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 $54.53   12.777%   $61.4973   $61.50   $61.50   $61.50  
  Purchase #2 $227.38   10.528%   $251.3186   $251.32   $251.30   $251.30  
  Purchase #3 $173.39   4.566%   $181.307   $181.31   $181.30   $181.30  
  Purchase #4 $60.31   4.359%   $62.9389   $62.94   $62.95   $62.90  
  Purchase #5 $176.96   10.161%   $194.9409   $194.94   $194.95   $194.90  
  Purchase #6 $151.31   4.287%   $157.7967   $157.80   $157.80   $157.80  
  Purchase #7 $66.51   13.651%   $75.5893   $75.59   $75.60   $75.60  
  7 purchase totals = $910.39       $985.3887   $985.40   $985.40   $985.30