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 $204.84   5.258%   $215.6105   $215.61   $215.60   $215.60  
  Purchase #2 $29.94   8.734%   $32.555   $32.56   $32.55   $32.60  
  Purchase #3 $39.87   10.636%   $44.1106   $44.11   $44.10   $44.10  
  Purchase #4 $179.63   4.600%   $187.893   $187.89   $187.90   $187.90  
  Purchase #5 $196.38   6.105%   $208.369   $208.37   $208.35   $208.40  
  Purchase #6 $69.49   10.515%   $76.7969   $76.80   $76.80   $76.80  
  Purchase #7 $236.92   12.403%   $266.3052   $266.31   $266.30   $266.30  
  7 purchase totals = $957.07       $1,031.6402   $1,031.65   $1,031.60   $1,031.70