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 $209.72   9.496%   $229.635   $229.64   $229.65   $229.60  
  Purchase #2 $159.34   13.535%   $180.9067   $180.91   $180.90   $180.90  
  Purchase #3 $151.95   3.482%   $157.2409   $157.24   $157.25   $157.20  
  Purchase #4 $29.69   9.438%   $32.4921   $32.49   $32.50   $32.50  
  Purchase #5 $201.26   5.637%   $212.605   $212.61   $212.60   $212.60  
  Purchase #6 $181.96   8.548%   $197.5139   $197.51   $197.50   $197.50  
  Purchase #7 $14.75   8.762%   $16.0424   $16.04   $16.05   $16.00  
  7 purchase totals = $948.67       $1,026.4360   $1,026.44   $1,026.45   $1,026.30