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 $85.49   13.458%   $96.9952   $97.00   $97.00   $97.00  
  Purchase #2 $185.61   11.597%   $207.1352   $207.14   $207.15   $207.10  
  Purchase #3 $19.61   13.309%   $22.2199   $22.22   $22.20   $22.20  
  Purchase #4 $98.38   11.608%   $109.8   $109.80   $109.80   $109.80  
  Purchase #5 $218.42   7.279%   $234.3188   $234.32   $234.30   $234.30  
  Purchase #6 $13.86   3.470%   $14.3409   $14.34   $14.35   $14.30  
  Purchase #7 $210.86   4.243%   $219.8068   $219.81   $219.80   $219.80  
  7 purchase totals = $832.23       $904.6168   $904.63   $904.60   $904.50