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 $248.28   5.848%   $262.7994   $262.80   $262.80   $262.80  
  Purchase #2 $37.35   4.213%   $38.9236   $38.92   $38.90   $38.90  
  Purchase #3 $175.37   11.244%   $195.0886   $195.09   $195.10   $195.10  
  Purchase #4 $10.96   11.496%   $12.22   $12.22   $12.20   $12.20  
  Purchase #5 $242.63   3.518%   $251.1657   $251.17   $251.15   $251.20  
  Purchase #6 $131.64   5.254%   $138.5564   $138.56   $138.55   $138.60  
  Purchase #7 $153.26   7.249%   $164.3698   $164.37   $164.35   $164.40  
  7 purchase totals = $999.49       $1,063.1235   $1,063.13   $1,063.05   $1,063.20