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 $145.56   5.271%   $153.2325   $153.23   $153.25   $153.20  
  Purchase #2 $67.72   8.619%   $73.5568   $73.56   $73.55   $73.60  
  Purchase #3 $115.43   8.840%   $125.634   $125.63   $125.65   $125.60  
  Purchase #4 $89.27   9.762%   $97.9845   $97.98   $98.00   $98.00  
  Purchase #5 $209.84   3.189%   $216.5318   $216.53   $216.55   $216.50  
  Purchase #6 $226.75   8.272%   $245.5068   $245.51   $245.50   $245.50  
  Purchase #7 $162.79   10.215%   $179.419   $179.42   $179.40   $179.40  
  7 purchase totals = $1,017.36       $1,091.8654   $1,091.86   $1,091.90   $1,091.80