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 $250.72   10.723%   $277.6047   $277.60   $277.60   $277.60  
  Purchase #2 $180.71   13.384%   $204.8962   $204.90   $204.90   $204.90  
  Purchase #3 $29.28   13.796%   $33.3195   $33.32   $33.30   $33.30  
  Purchase #4 $75.36   5.836%   $79.758   $79.76   $79.75   $79.80  
  Purchase #5 $106.39   7.418%   $114.282   $114.28   $114.30   $114.30  
  Purchase #6 $29.39   12.416%   $33.0391   $33.04   $33.05   $33.00  
  Purchase #7 $23.28   3.737%   $24.15   $24.15   $24.15   $24.20  
  7 purchase totals = $695.13       $767.0495   $767.05   $767.05   $767.10