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 $87.27   13.306%   $98.8821   $98.88   $98.90   $98.90  
  Purchase #2 $190.81   12.175%   $214.0411   $214.04   $214.05   $214.00  
  Purchase #3 $157.76   6.198%   $167.538   $167.54   $167.55   $167.50  
  Purchase #4 $116.29   7.598%   $125.1257   $125.13   $125.15   $125.10  
  Purchase #5 $207.44   8.332%   $224.7239   $224.72   $224.70   $224.70  
  Purchase #6 $211.29   3.747%   $219.207   $219.21   $219.20   $219.20  
  Purchase #7 $104.79   13.393%   $118.8245   $118.82   $118.80   $118.80  
  7 purchase totals = $1,075.65       $1,168.3423   $1,168.34   $1,168.35   $1,168.20