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 $208.91   10.673%   $231.207   $231.21   $231.20   $231.20  
  Purchase #2 $50.36   4.472%   $52.6121   $52.61   $52.60   $52.60  
  Purchase #3 $41.40   12.682%   $46.6503   $46.65   $46.65   $46.70  
  Purchase #4 $19.91   7.772%   $21.4574   $21.46   $21.45   $21.50  
  Purchase #5 $104.40   10.394%   $115.2513   $115.25   $115.25   $115.30  
  Purchase #6 $120.50   6.720%   $128.5976   $128.60   $128.60   $128.60  
  Purchase #7 $150.71   4.530%   $157.5372   $157.54   $157.55   $157.50  
  7 purchase totals = $696.19       $753.3129   $753.32   $753.30   $753.40