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 $206.64   7.208%   $221.5346   $221.53   $221.55   $221.50  
  Purchase #2 $168.69   13.822%   $192.0063   $192.01   $192.00   $192.00  
  Purchase #3 $167.71   5.321%   $176.6338   $176.63   $176.65   $176.60  
  Purchase #4 $148.60   12.862%   $167.7129   $167.71   $167.70   $167.70  
  Purchase #5 $48.59   10.264%   $53.5773   $53.58   $53.60   $53.60  
  Purchase #6 $176.64   12.831%   $199.3047   $199.30   $199.30   $199.30  
  Purchase #7 $9.86   4.379%   $10.2918   $10.29   $10.30   $10.30  
  7 purchase totals = $926.73       $1,021.0614   $1,021.05   $1,021.10   $1,021.00