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 $89.51   9.643%   $98.1414   $98.14   $98.15   $98.10  
  Purchase #2 $74.37   11.149%   $82.6615   $82.66   $82.65   $82.70  
  Purchase #3 $249.37   9.424%   $272.8706   $272.87   $272.85   $272.90  
  Purchase #4 $75.35   9.166%   $82.2566   $82.26   $82.25   $82.30  
  Purchase #5 $242.51   11.849%   $271.245   $271.25   $271.25   $271.20  
  Purchase #6 $116.74   7.872%   $125.9298   $125.93   $125.95   $125.90  
  Purchase #7 $168.42   8.324%   $182.4393   $182.44   $182.45   $182.40  
  7 purchase totals = $1,016.27       $1,115.5442   $1,115.55   $1,115.55   $1,115.50