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 $61.93   11.233%   $68.8866   $68.89   $68.90   $68.90  
  Purchase #2 $85.63   10.235%   $94.3942   $94.39   $94.40   $94.40  
  Purchase #3 $104.76   4.452%   $109.4239   $109.42   $109.40   $109.40  
  Purchase #4 $80.30   9.449%   $87.8875   $87.89   $87.90   $87.90  
  Purchase #5 $121.53   13.321%   $137.719   $137.72   $137.70   $137.70  
  Purchase #6 $31.76   10.329%   $35.0405   $35.04   $35.05   $35.00  
  Purchase #7 $26.75   10.787%   $29.6355   $29.64   $29.65   $29.60  
  7 purchase totals = $512.66       $562.9872   $562.99   $563.00   $562.90