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 $41.31   7.271%   $44.3137   $44.31   $44.30   $44.30  
  Purchase #2 $31.28   11.783%   $34.9657   $34.97   $34.95   $35.00  
  Purchase #3 $42.46   6.413%   $45.183   $45.18   $45.20   $45.20  
  Purchase #4 $44.99   3.134%   $46.4   $46.40   $46.40   $46.40  
  Purchase #5 $98.64   6.363%   $104.9165   $104.92   $104.90   $104.90  
  Purchase #6 $116.58   3.630%   $120.8119   $120.81   $120.80   $120.80  
  Purchase #7 $208.36   10.742%   $230.742   $230.74   $230.75   $230.70  
  7 purchase totals = $583.62       $627.3328   $627.33   $627.30   $627.30