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 $237.61   13.232%   $269.0506   $269.05   $269.05   $269.10  
  Purchase #2 $95.34   8.824%   $103.7528   $103.75   $103.75   $103.80  
  Purchase #3 $183.45   11.789%   $205.0769   $205.08   $205.10   $205.10  
  Purchase #4 $14.90   11.226%   $16.5727   $16.57   $16.55   $16.60  
  Purchase #5 $54.56   10.636%   $60.363   $60.36   $60.35   $60.40  
  Purchase #6 $34.76   12.781%   $39.2027   $39.20   $39.20   $39.20  
  Purchase #7 $101.96   12.196%   $114.395   $114.40   $114.40   $114.40  
  7 purchase totals = $722.58       $808.4137   $808.41   $808.40   $808.60