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 $138.26   5.853%   $146.3524   $146.35   $146.35   $146.40  
  Purchase #2 $242.80   10.281%   $267.7623   $267.76   $267.75   $267.80  
  Purchase #3 $44.28   9.747%   $48.596   $48.60   $48.60   $48.60  
  Purchase #4 $90.65   7.321%   $97.2865   $97.29   $97.30   $97.30  
  Purchase #5 $59.41   11.393%   $66.1786   $66.18   $66.20   $66.20  
  Purchase #6 $151.58   9.578%   $166.0983   $166.10   $166.10   $166.10  
  Purchase #7 $84.27   7.572%   $90.6509   $90.65   $90.65   $90.70  
  7 purchase totals = $811.25       $882.9250   $882.93   $882.95   $883.10