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 $205.53   10.302%   $226.7037   $226.70   $226.70   $226.70  
  Purchase #2 $189.45   4.347%   $197.6854   $197.69   $197.70   $197.70  
  Purchase #3 $159.51   8.791%   $173.5325   $173.53   $173.55   $173.50  
  Purchase #4 $169.83   11.489%   $189.3418   $189.34   $189.35   $189.30  
  Purchase #5 $128.58   4.317%   $134.1308   $134.13   $134.15   $134.10  
  Purchase #6 $214.47   7.863%   $231.3338   $231.33   $231.35   $231.30  
  Purchase #7 $239.86   4.756%   $251.2677   $251.27   $251.25   $251.30  
  7 purchase totals = $1,307.23       $1,403.9957   $1,403.99   $1,404.05   $1,403.90