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 $208.49   6.563%   $222.1732   $222.17   $222.15   $222.20  
  Purchase #2 $46.62   10.612%   $51.5673   $51.57   $51.55   $51.60  
  Purchase #3 $184.67   3.181%   $190.5444   $190.54   $190.55   $190.50  
  Purchase #4 $24.41   12.133%   $27.3717   $27.37   $27.35   $27.40  
  Purchase #5 $233.82   4.367%   $244.0309   $244.03   $244.05   $244.00  
  Purchase #6 $223.34   3.420%   $230.9782   $230.98   $231.00   $231.00  
  Purchase #7 $42.55   12.782%   $47.9887   $47.99   $48.00   $48.00  
  7 purchase totals = $963.90       $1,014.6544   $1,014.65   $1,014.65   $1,014.70