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 $229.93   8.228%   $248.8486   $248.85   $248.85   $248.80  
  Purchase #2 $192.90   4.279%   $201.1542   $201.15   $201.15   $201.20  
  Purchase #3 $54.45   5.411%   $57.3963   $57.40   $57.40   $57.40  
  Purchase #4 $233.88   7.367%   $251.1099   $251.11   $251.10   $251.10  
  Purchase #5 $20.80   10.682%   $23.0219   $23.02   $23.00   $23.00  
  Purchase #6 $69.95   12.816%   $78.9148   $78.91   $78.90   $78.90  
  Purchase #7 $137.99   11.787%   $154.2549   $154.25   $154.25   $154.30  
  7 purchase totals = $939.90       $1,014.7006   $1,014.69   $1,014.65   $1,014.70