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 $44.66   6.264%   $47.4575   $47.46   $47.45   $47.50  
  Purchase #2 $118.97   4.219%   $123.9893   $123.99   $124.00   $124.00  
  Purchase #3 $187.42   5.226%   $197.2146   $197.21   $197.20   $197.20  
  Purchase #4 $196.95   4.685%   $206.1771   $206.18   $206.20   $206.20  
  Purchase #5 $69.57   10.506%   $76.879   $76.88   $76.90   $76.90  
  Purchase #6 $91.80   3.641%   $95.1424   $95.14   $95.15   $95.10  
  Purchase #7 $152.76   10.676%   $169.0687   $169.07   $169.05   $169.10  
  7 purchase totals = $862.13       $915.9286   $915.93   $915.95   $916.00