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 $212.37   6.184%   $225.503   $225.50   $225.50   $225.50  
  Purchase #2 $11.27   8.746%   $12.2557   $12.26   $12.25   $12.30  
  Purchase #3 $64.69   6.398%   $68.8289   $68.83   $68.85   $68.80  
  Purchase #4 $59.97   4.520%   $62.6806   $62.68   $62.70   $62.70  
  Purchase #5 $58.74   9.216%   $64.1535   $64.15   $64.15   $64.20  
  Purchase #6 $232.38   8.171%   $251.3678   $251.37   $251.35   $251.40  
  Purchase #7 $225.64   4.177%   $235.065   $235.07   $235.05   $235.10  
  7 purchase totals = $865.06       $919.8545   $919.86   $919.85   $920.00