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 $249.81   6.402%   $265.8028   $265.80   $265.80   $265.80  
  Purchase #2 $214.37   10.472%   $236.8188   $236.82   $236.80   $236.80  
  Purchase #3 $44.32   6.596%   $47.2433   $47.24   $47.25   $47.20  
  Purchase #4 $93.85   10.776%   $103.9633   $103.96   $103.95   $104.00  
  Purchase #5 $16.31   5.763%   $17.2499   $17.25   $17.25   $17.20  
  Purchase #6 $64.77   3.505%   $67.0402   $67.04   $67.05   $67.00  
  Purchase #7 $212.90   4.850%   $223.2257   $223.23   $223.25   $223.20  
  7 purchase totals = $896.33       $961.3440   $961.34   $961.35   $961.20