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 $246.57   3.112%   $254.2433   $254.24   $254.25   $254.20  
  Purchase #2 $196.87   10.667%   $217.8701   $217.87   $217.85   $217.90  
  Purchase #3 $104.38   10.184%   $115.0101   $115.01   $115.00   $115.00  
  Purchase #4 $23.60   3.455%   $24.4154   $24.42   $24.40   $24.40  
  Purchase #5 $208.64   11.777%   $233.2115   $233.21   $233.20   $233.20  
  Purchase #6 $55.55   5.256%   $58.4697   $58.47   $58.45   $58.50  
  Purchase #7 $142.73   12.808%   $161.0109   $161.01   $161.00   $161.00  
  7 purchase totals = $978.34       $1,064.2310   $1,064.23   $1,064.15   $1,064.20