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 $68.42   4.723%   $71.6515   $71.65   $71.65   $71.70  
  Purchase #2 $173.90   11.661%   $194.1785   $194.18   $194.20   $194.20  
  Purchase #3 $239.30   8.278%   $259.1093   $259.11   $259.10   $259.10  
  Purchase #4 $78.72   4.652%   $82.3821   $82.38   $82.40   $82.40  
  Purchase #5 $229.57   12.576%   $258.4407   $258.44   $258.45   $258.40  
  Purchase #6 $14.50   13.177%   $16.4107   $16.41   $16.40   $16.40  
  Purchase #7 $217.63   7.797%   $234.5986   $234.60   $234.60   $234.60  
  7 purchase totals = $1,022.04       $1,116.7714   $1,116.77   $1,116.80   $1,116.80