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 $166.51   11.561%   $185.7602   $185.76   $185.75   $185.80  
  Purchase #2 $247.41   4.247%   $257.9175   $257.92   $257.90   $257.90  
  Purchase #3 $17.81   10.231%   $19.6321   $19.63   $19.65   $19.60  
  Purchase #4 $245.89   13.763%   $279.7318   $279.73   $279.75   $279.70  
  Purchase #5 $246.69   12.426%   $277.3437   $277.34   $277.35   $277.30  
  Purchase #6 $178.84   8.371%   $193.8107   $193.81   $193.80   $193.80  
  Purchase #7 $182.88   8.192%   $197.8615   $197.86   $197.85   $197.90  
  7 purchase totals = $1,286.03       $1,412.0575   $1,412.05   $1,412.05   $1,412.00