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 $236.94   5.372%   $249.6684   $249.67   $249.65   $249.70  
  Purchase #2 $213.37   6.195%   $226.5883   $226.59   $226.60   $226.60  
  Purchase #3 $174.47   13.416%   $197.8769   $197.88   $197.90   $197.90  
  Purchase #4 $198.39   3.231%   $204.8   $204.80   $204.80   $204.80  
  Purchase #5 $182.60   3.184%   $188.414   $188.41   $188.40   $188.40  
  Purchase #6 $125.61   6.468%   $133.7345   $133.73   $133.75   $133.70  
  Purchase #7 $242.25   10.448%   $267.5603   $267.56   $267.55   $267.60  
  7 purchase totals = $1,373.63       $1,468.6424   $1,468.64   $1,468.65   $1,468.70