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 $233.62   10.779%   $258.8019   $258.80   $258.80   $258.80  
  Purchase #2 $191.70   6.521%   $204.2008   $204.20   $204.20   $204.20  
  Purchase #3 $248.26   8.635%   $269.6973   $269.70   $269.70   $269.70  
  Purchase #4 $76.65   8.373%   $83.0679   $83.07   $83.05   $83.10  
  Purchase #5 $124.35   13.505%   $141.1435   $141.14   $141.15   $141.10  
  Purchase #6 $64.39   11.430%   $71.7498   $71.75   $71.75   $71.70  
  Purchase #7 $146.69   6.479%   $156.194   $156.19   $156.20   $156.20  
  7 purchase totals = $1,085.66       $1,184.8552   $1,184.85   $1,184.85   $1,184.80