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 $244.42   10.383%   $269.7981   $269.80   $269.80   $269.80  
  Purchase #2 $179.75   8.330%   $194.7232   $194.72   $194.70   $194.70  
  Purchase #3 $240.62   3.551%   $249.1644   $249.16   $249.15   $249.20  
  Purchase #4 $98.45   5.272%   $103.6403   $103.64   $103.65   $103.60  
  Purchase #5 $212.31   10.136%   $233.8297   $233.83   $233.85   $233.80  
  Purchase #6 $148.48   13.787%   $168.9509   $168.95   $168.95   $169.00  
  Purchase #7 $58.41   5.860%   $61.8328   $61.83   $61.85   $61.80  
  7 purchase totals = $1,182.44       $1,281.9394   $1,281.93   $1,281.95   $1,281.90