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 $98.90   4.407%   $103.2585   $103.26   $103.25   $103.30  
  Purchase #2 $28.48   5.686%   $30.0994   $30.10   $30.10   $30.10  
  Purchase #3 $173.50   4.415%   $181.16   $181.16   $181.15   $181.20  
  Purchase #4 $65.75   7.803%   $70.8805   $70.88   $70.90   $70.90  
  Purchase #5 $78.54   10.551%   $86.8268   $86.83   $86.85   $86.80  
  Purchase #6 $18.62   3.804%   $19.3283   $19.33   $19.35   $19.30  
  Purchase #7 $142.98   5.557%   $150.9254   $150.93   $150.95   $150.90  
  7 purchase totals = $606.77       $642.4789   $642.49   $642.55   $642.50