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 $246.87   7.652%   $265.7605   $265.76   $265.75   $265.80  
  Purchase #2 $247.39   6.672%   $263.8959   $263.90   $263.90   $263.90  
  Purchase #3 $116.26   9.138%   $126.8838   $126.88   $126.90   $126.90  
  Purchase #4 $196.46   11.109%   $218.2847   $218.28   $218.30   $218.30  
  Purchase #5 $134.90   8.195%   $145.9551   $145.96   $145.95   $146.00  
  Purchase #6 $229.85   10.861%   $254.814   $254.81   $254.80   $254.80  
  Purchase #7 $232.86   6.859%   $248.8319   $248.83   $248.85   $248.80  
  7 purchase totals = $1,404.59       $1,524.4259   $1,524.42   $1,524.45   $1,524.50