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 $11.48   5.503%   $12.1117   $12.11   $12.10   $12.10  
  Purchase #2 $161.73   10.161%   $178.1634   $178.16   $178.15   $178.20  
  Purchase #3 $80.43   12.520%   $90.4998   $90.50   $90.50   $90.50  
  Purchase #4 $249.99   8.543%   $271.3466   $271.35   $271.35   $271.30  
  Purchase #5 $104.70   3.744%   $108.62   $108.62   $108.60   $108.60  
  Purchase #6 $109.67   9.266%   $119.832   $119.83   $119.85   $119.80  
  Purchase #7 $242.84   9.627%   $266.2182   $266.22   $266.20   $266.20  
  7 purchase totals = $960.84       $1,046.7917   $1,046.79   $1,046.75   $1,046.70