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 $96.53   7.389%   $103.6626   $103.66   $103.65   $103.70  
  Purchase #2 $234.76   12.869%   $264.9713   $264.97   $264.95   $265.00  
  Purchase #3 $248.83   11.742%   $278.0476   $278.05   $278.05   $278.00  
  Purchase #4 $195.72   8.707%   $212.7613   $212.76   $212.75   $212.80  
  Purchase #5 $159.92   5.293%   $168.3846   $168.38   $168.40   $168.40  
  Purchase #6 $47.90   9.678%   $52.5358   $52.54   $52.55   $52.50  
  Purchase #7 $198.83   5.307%   $209.3819   $209.38   $209.40   $209.40  
  7 purchase totals = $1,182.49       $1,289.7451   $1,289.74   $1,289.75   $1,289.80