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 $104.53   8.746%   $113.6722   $113.67   $113.65   $113.70  
  Purchase #2 $234.49   13.412%   $265.9398   $265.94   $265.95   $265.90  
  Purchase #3 $64.59   8.185%   $69.8767   $69.88   $69.90   $69.90  
  Purchase #4 $110.92   12.267%   $124.5266   $124.53   $124.55   $124.50  
  Purchase #5 $162.88   7.727%   $175.4657   $175.47   $175.45   $175.50  
  Purchase #6 $142.65   13.266%   $161.5739   $161.57   $161.55   $161.60  
  Purchase #7 $226.45   10.485%   $250.1933   $250.19   $250.20   $250.20  
  7 purchase totals = $1,046.51       $1,161.2482   $1,161.25   $1,161.25   $1,161.30