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 $62.26   8.642%   $67.6405   $67.64   $67.65   $67.60  
  Purchase #2 $146.46   13.430%   $166.1296   $166.13   $166.15   $166.10  
  Purchase #3 $123.27   12.188%   $138.2941   $138.29   $138.30   $138.30  
  Purchase #4 $181.77   7.374%   $195.1737   $195.17   $195.15   $195.20  
  Purchase #5 $10.93   8.154%   $11.8212   $11.82   $11.80   $11.80  
  Purchase #6 $161.50   8.866%   $175.8186   $175.82   $175.80   $175.80  
  Purchase #7 $143.78   5.246%   $151.3227   $151.32   $151.30   $151.30  
  7 purchase totals = $829.97       $906.2004   $906.19   $906.15   $906.10