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 $243.61   10.498%   $269.1842   $269.18   $269.20   $269.20  
  Purchase #2 $172.85   6.858%   $184.7041   $184.70   $184.70   $184.70  
  Purchase #3 $80.51   8.220%   $87.1279   $87.13   $87.15   $87.10  
  Purchase #4 $108.40   5.602%   $114.4726   $114.47   $114.45   $114.50  
  Purchase #5 $15.25   9.439%   $16.6894   $16.69   $16.70   $16.70  
  Purchase #6 $210.64   3.629%   $218.2841   $218.28   $218.30   $218.30  
  Purchase #7 $147.75   12.290%   $165.9085   $165.91   $165.90   $165.90  
  7 purchase totals = $979.01       $1,056.3708   $1,056.36   $1,056.40   $1,056.40