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 $91.55   5.106%   $96.2245   $96.22   $96.20   $96.20  
  Purchase #2 $230.30   6.597%   $245.4929   $245.49   $245.50   $245.50  
  Purchase #3 $52.29   10.439%   $57.7486   $57.75   $57.75   $57.70  
  Purchase #4 $164.47   4.174%   $171.335   $171.34   $171.35   $171.30  
  Purchase #5 $206.79   10.168%   $227.8164   $227.82   $227.80   $227.80  
  Purchase #6 $66.30   10.613%   $73.3364   $73.34   $73.35   $73.30  
  Purchase #7 $236.78   5.315%   $249.3649   $249.36   $249.35   $249.40  
  7 purchase totals = $1,048.48       $1,121.3187   $1,121.32   $1,121.30   $1,121.20