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 $191.97   7.623%   $206.6039   $206.60   $206.60   $206.60  
  Purchase #2 $89.65   5.426%   $94.5144   $94.51   $94.50   $94.50  
  Purchase #3 $181.53   9.786%   $199.2945   $199.29   $199.30   $199.30  
  Purchase #4 $22.26   8.539%   $24.1608   $24.16   $24.15   $24.20  
  Purchase #5 $241.39   6.564%   $257.2348   $257.23   $257.25   $257.20  
  Purchase #6 $176.93   9.235%   $193.2695   $193.27   $193.25   $193.30  
  Purchase #7 $245.44   9.446%   $268.6243   $268.62   $268.60   $268.60  
  7 purchase totals = $1,149.17       $1,243.7022   $1,243.68   $1,243.65   $1,243.70