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 $236.78   13.770%   $269.3846   $269.38   $269.40   $269.40  
  Purchase #2 $214.66   10.613%   $237.4419   $237.44   $237.45   $237.40  
  Purchase #3 $167.91   5.350%   $176.8932   $176.89   $176.90   $176.90  
  Purchase #4 $203.93   10.432%   $225.204   $225.20   $225.20   $225.20  
  Purchase #5 $225.72   6.758%   $240.9742   $240.97   $240.95   $241.00  
  Purchase #6 $192.49   5.223%   $202.5438   $202.54   $202.55   $202.50  
  Purchase #7 $84.41   12.197%   $94.7055   $94.71   $94.70   $94.70  
  7 purchase totals = $1,325.90       $1,447.1472   $1,447.13   $1,447.15   $1,447.10