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 $248.96   8.136%   $269.2154   $269.22   $269.20   $269.20  
  Purchase #2 $82.61   7.122%   $88.4935   $88.49   $88.50   $88.50  
  Purchase #3 $168.44   12.247%   $189.0688   $189.07   $189.05   $189.10  
  Purchase #4 $87.45   12.183%   $98.104   $98.10   $98.10   $98.10  
  Purchase #5 $43.35   12.377%   $48.7154   $48.72   $48.70   $48.70  
  Purchase #6 $130.91   13.141%   $148.1129   $148.11   $148.10   $148.10  
  Purchase #7 $204.76   8.276%   $221.7059   $221.71   $221.70   $221.70  
  7 purchase totals = $966.48       $1,063.4159   $1,063.42   $1,063.35   $1,063.40