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 $104.39   9.771%   $114.5899   $114.59   $114.60   $114.60  
  Purchase #2 $190.66   6.347%   $202.7612   $202.76   $202.75   $202.80  
  Purchase #3 $31.47   6.554%   $33.5325   $33.53   $33.55   $33.50  
  Purchase #4 $108.71   10.827%   $120.48   $120.48   $120.50   $120.50  
  Purchase #5 $73.35   13.235%   $83.0579   $83.06   $83.05   $83.10  
  Purchase #6 $56.94   3.711%   $59.053   $59.05   $59.05   $59.10  
  Purchase #7 $58.75   3.373%   $60.7316   $60.73   $60.75   $60.70  
  7 purchase totals = $624.27       $674.2061   $674.20   $674.25   $674.30