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 $248.97   7.349%   $267.2668   $267.27   $267.25   $267.30  
  Purchase #2 $151.76   9.298%   $165.8706   $165.87   $165.85   $165.90  
  Purchase #3 $216.43   5.663%   $228.6864   $228.69   $228.70   $228.70  
  Purchase #4 $153.49   5.725%   $162.2773   $162.28   $162.30   $162.30  
  Purchase #5 $43.35   6.336%   $46.0967   $46.10   $46.10   $46.10  
  Purchase #6 $217.37   12.354%   $244.2239   $244.22   $244.20   $244.20  
  Purchase #7 $216.37   13.434%   $245.4371   $245.44   $245.45   $245.40  
  7 purchase totals = $1,247.74       $1,359.8588   $1,359.87   $1,359.85   $1,359.90