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 $206.76   12.554%   $232.7167   $232.72   $232.70   $232.70  
  Purchase #2 $175.45   9.348%   $191.8511   $191.85   $191.85   $191.90  
  Purchase #3 $51.64   10.566%   $57.0963   $57.10   $57.10   $57.10  
  Purchase #4 $169.57   10.577%   $187.5054   $187.51   $187.50   $187.50  
  Purchase #5 $192.78   8.376%   $208.9273   $208.93   $208.95   $208.90  
  Purchase #6 $188.57   9.471%   $206.4295   $206.43   $206.45   $206.40  
  Purchase #7 $140.62   6.733%   $150.0879   $150.09   $150.10   $150.10  
  7 purchase totals = $1,125.39       $1,234.6142   $1,234.63   $1,234.65   $1,234.60