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 $104.57   13.673%   $118.8679   $118.87   $118.85   $118.90  
  Purchase #2 $200.62   10.390%   $221.4644   $221.46   $221.45   $221.50  
  Purchase #3 $241.85   8.434%   $262.2476   $262.25   $262.25   $262.20  
  Purchase #4 $157.55   12.413%   $177.1067   $177.11   $177.10   $177.10  
  Purchase #5 $196.28   3.291%   $202.7396   $202.74   $202.75   $202.70  
  Purchase #6 $20.41   7.662%   $21.9738   $21.97   $21.95   $22.00  
  Purchase #7 $114.28   5.518%   $120.586   $120.59   $120.60   $120.60  
  7 purchase totals = $1,035.56       $1,124.9860   $1,124.99   $1,124.95   $1,125.00