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 $50.37   9.261%   $55.0348   $55.03   $55.05   $55.00  
  Purchase #2 $107.92   9.587%   $118.2663   $118.27   $118.25   $118.30  
  Purchase #3 $169.38   3.850%   $175.9011   $175.90   $175.90   $175.90  
  Purchase #4 $108.82   6.733%   $116.1469   $116.15   $116.15   $116.10  
  Purchase #5 $125.76   8.577%   $136.5464   $136.55   $136.55   $136.50  
  Purchase #6 $201.95   10.520%   $223.1951   $223.20   $223.20   $223.20  
  Purchase #7 $178.42   6.139%   $189.3732   $189.37   $189.35   $189.40  
  7 purchase totals = $942.62       $1,014.4638   $1,014.47   $1,014.45   $1,014.40