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 $43.59   13.715%   $49.5684   $49.57   $49.55   $49.60  
  Purchase #2 $41.77   13.575%   $47.4403   $47.44   $47.45   $47.40  
  Purchase #3 $213.70   4.800%   $223.9576   $223.96   $223.95   $224.00  
  Purchase #4 $121.65   12.548%   $136.9146   $136.91   $136.90   $136.90  
  Purchase #5 $130.65   5.432%   $137.7469   $137.75   $137.75   $137.70  
  Purchase #6 $149.58   8.423%   $162.1791   $162.18   $162.20   $162.20  
  Purchase #7 $186.82   5.559%   $197.2053   $197.21   $197.20   $197.20  
  7 purchase totals = $887.76       $955.0122   $955.02   $955.00   $955.00