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 $241.27   6.126%   $256.0502   $256.05   $256.05   $256.10  
  Purchase #2 $222.93   10.417%   $246.1526   $246.15   $246.15   $246.20  
  Purchase #3 $23.48   12.866%   $26.5009   $26.50   $26.50   $26.50  
  Purchase #4 $224.46   13.547%   $254.8676   $254.87   $254.85   $254.90  
  Purchase #5 $59.93   5.147%   $63.0146   $63.01   $63.00   $63.00  
  Purchase #6 $100.87   3.871%   $104.7747   $104.77   $104.75   $104.80  
  Purchase #7 $127.40   8.232%   $137.8876   $137.89   $137.90   $137.90  
  7 purchase totals = $1,000.34       $1,089.2482   $1,089.24   $1,089.20   $1,089.40