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 $56.26   12.519%   $63.3032   $63.30   $63.30   $63.30  
  Purchase #2 $170.39   3.806%   $176.875   $176.88   $176.90   $176.90  
  Purchase #3 $141.77   13.749%   $161.262   $161.26   $161.25   $161.30  
  Purchase #4 $194.86   10.128%   $214.5954   $214.60   $214.60   $214.60  
  Purchase #5 $195.44   3.672%   $202.6166   $202.62   $202.60   $202.60  
  Purchase #6 $206.72   3.579%   $214.1185   $214.12   $214.10   $214.10  
  Purchase #7 $6.57   5.640%   $6.9405   $6.94   $6.95   $6.90  
  7 purchase totals = $972.01       $1,039.7112   $1,039.72   $1,039.70   $1,039.70