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 $167.67   5.289%   $176.5381   $176.54   $176.55   $176.50  
  Purchase #2 $213.55   13.220%   $241.7813   $241.78   $241.80   $241.80  
  Purchase #3 $96.90   13.448%   $109.9311   $109.93   $109.95   $109.90  
  Purchase #4 $95.79   12.472%   $107.7369   $107.74   $107.75   $107.70  
  Purchase #5 $162.49   4.643%   $170.0344   $170.03   $170.05   $170.00  
  Purchase #6 $157.70   6.178%   $167.4427   $167.44   $167.45   $167.40  
  Purchase #7 $95.38   3.300%   $98.5275   $98.53   $98.55   $98.50  
  7 purchase totals = $989.48       $1,071.9920   $1,071.99   $1,072.10   $1,071.80