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 $233.82   3.698%   $242.4667   $242.47   $242.45   $242.50  
  Purchase #2 $216.57   13.575%   $245.9694   $245.97   $245.95   $246.00  
  Purchase #3 $47.67   6.841%   $50.9311   $50.93   $50.95   $50.90  
  Purchase #4 $76.79   3.210%   $79.255   $79.26   $79.25   $79.30  
  Purchase #5 $95.99   12.549%   $108.0358   $108.04   $108.05   $108.00  
  Purchase #6 $94.71   11.340%   $105.4501   $105.45   $105.45   $105.50  
  Purchase #7 $249.66   6.446%   $265.7531   $265.75   $265.75   $265.80  
  7 purchase totals = $1,015.21       $1,097.8612   $1,097.87   $1,097.85   $1,098.00