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 $164.80   7.147%   $176.5783   $176.58   $176.60   $176.60  
  Purchase #2 $208.61   4.794%   $218.6108   $218.61   $218.60   $218.60  
  Purchase #3 $105.96   13.145%   $119.8884   $119.89   $119.90   $119.90  
  Purchase #4 $201.56   4.493%   $210.6161   $210.62   $210.60   $210.60  
  Purchase #5 $113.86   5.259%   $119.8479   $119.85   $119.85   $119.80  
  Purchase #6 $204.61   4.471%   $213.7581   $213.76   $213.75   $213.80  
  Purchase #7 $245.51   9.753%   $269.4546   $269.45   $269.45   $269.50  
  7 purchase totals = $1,244.91       $1,328.7542   $1,328.76   $1,328.75   $1,328.80