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 $161.90   8.561%   $175.7603   $175.76   $175.75   $175.80  
  Purchase #2 $209.80   4.321%   $218.8655   $218.87   $218.85   $218.90  
  Purchase #3 $82.46   12.292%   $92.596   $92.60   $92.60   $92.60  
  Purchase #4 $217.33   11.172%   $241.6101   $241.61   $241.60   $241.60  
  Purchase #5 $211.25   13.329%   $239.4075   $239.41   $239.40   $239.40  
  Purchase #6 $66.67   12.440%   $74.9637   $74.96   $74.95   $75.00  
  Purchase #7 $14.34   12.171%   $16.0853   $16.09   $16.10   $16.10  
  7 purchase totals = $963.75       $1,059.2884   $1,059.30   $1,059.25   $1,059.40