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 $206.93   9.288%   $226.1497   $226.15   $226.15   $226.10  
  Purchase #2 $10.59   11.365%   $11.7936   $11.79   $11.80   $11.80  
  Purchase #3 $154.81   7.665%   $166.6762   $166.68   $166.70   $166.70  
  Purchase #4 $221.91   8.585%   $240.961   $240.96   $240.95   $241.00  
  Purchase #5 $188.53   13.136%   $213.2953   $213.30   $213.30   $213.30  
  Purchase #6 $110.55   6.711%   $117.969   $117.97   $117.95   $118.00  
  Purchase #7 $59.64   13.245%   $67.5393   $67.54   $67.55   $67.50  
  7 purchase totals = $952.96       $1,044.3841   $1,044.39   $1,044.40   $1,044.40