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 $175.67   13.540%   $199.4557   $199.46   $199.45   $199.50  
  Purchase #2 $47.63   9.544%   $52.1758   $52.18   $52.20   $52.20  
  Purchase #3 $242.49   10.693%   $268.4195   $268.42   $268.40   $268.40  
  Purchase #4 $176.71   12.501%   $198.8005   $198.80   $198.80   $198.80  
  Purchase #5 $9.40   10.505%   $10.3875   $10.39   $10.40   $10.40  
  Purchase #6 $109.66   9.323%   $119.8836   $119.88   $119.90   $119.90  
  Purchase #7 $119.99   8.729%   $130.4639   $130.46   $130.45   $130.50  
  7 purchase totals = $881.55       $979.5865   $979.59   $979.60   $979.70