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 $98.92   9.366%   $108.1848   $108.18   $108.20   $108.20  
  Purchase #2 $91.60   10.150%   $100.8974   $100.90   $100.90   $100.90  
  Purchase #3 $208.94   10.604%   $231.096   $231.10   $231.10   $231.10  
  Purchase #4 $19.43   5.660%   $20.5297   $20.53   $20.55   $20.50  
  Purchase #5 $39.64   13.357%   $44.9347   $44.93   $44.95   $44.90  
  Purchase #6 $28.26   3.559%   $29.2658   $29.27   $29.25   $29.30  
  Purchase #7 $39.63   13.306%   $44.9032   $44.90   $44.90   $44.90  
  7 purchase totals = $526.42       $579.8116   $579.81   $579.85   $579.80