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 $244.82   6.605%   $260.9904   $260.99   $261.00   $261.00  
  Purchase #2 $138.59   4.237%   $144.4621   $144.46   $144.45   $144.50  
  Purchase #3 $93.73   10.210%   $103.2998   $103.30   $103.30   $103.30  
  Purchase #4 $240.63   10.725%   $266.4376   $266.44   $266.45   $266.40  
  Purchase #5 $202.51   8.289%   $219.2961   $219.30   $219.30   $219.30  
  Purchase #6 $11.46   12.635%   $12.908   $12.91   $12.90   $12.90  
  Purchase #7 $205.96   13.300%   $233.3527   $233.35   $233.35   $233.40  
  7 purchase totals = $1,137.70       $1,240.7467   $1,240.75   $1,240.75   $1,240.80