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 $242.46   10.298%   $267.4285   $267.43   $267.45   $267.40  
  Purchase #2 $244.98   7.572%   $263.5299   $263.53   $263.55   $263.50  
  Purchase #3 $142.65   12.781%   $160.8821   $160.88   $160.90   $160.90  
  Purchase #4 $30.29   12.745%   $34.1505   $34.15   $34.15   $34.20  
  Purchase #5 $61.31   7.718%   $66.0419   $66.04   $66.05   $66.00  
  Purchase #6 $226.70   6.685%   $241.8549   $241.85   $241.85   $241.90  
  Purchase #7 $114.93   3.723%   $119.2088   $119.21   $119.20   $119.20  
  7 purchase totals = $1,063.32       $1,153.0966   $1,153.09   $1,153.15   $1,153.10