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 $163.89   13.618%   $186.2085   $186.21   $186.20   $186.20  
  Purchase #2 $53.84   13.131%   $60.9097   $60.91   $60.90   $60.90  
  Purchase #3 $123.66   12.324%   $138.8999   $138.90   $138.90   $138.90  
  Purchase #4 $18.80   7.729%   $20.2531   $20.25   $20.25   $20.30  
  Purchase #5 $179.47   8.862%   $195.3746   $195.37   $195.35   $195.40  
  Purchase #6 $88.25   8.211%   $95.4962   $95.50   $95.50   $95.50  
  Purchase #7 $85.89   10.797%   $95.1635   $95.16   $95.15   $95.20  
  7 purchase totals = $713.80       $792.3055   $792.30   $792.25   $792.40