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 $165.62   12.530%   $186.3722   $186.37   $186.35   $186.40  
  Purchase #2 $227.84   13.180%   $257.8693   $257.87   $257.85   $257.90  
  Purchase #3 $119.67   11.868%   $133.8724   $133.87   $133.85   $133.90  
  Purchase #4 $44.87   4.205%   $46.7568   $46.76   $46.75   $46.80  
  Purchase #5 $22.97   10.698%   $25.4273   $25.43   $25.45   $25.40  
  Purchase #6 $206.54   7.594%   $222.2246   $222.22   $222.20   $222.20  
  Purchase #7 $170.76   8.745%   $185.693   $185.69   $185.70   $185.70  
  7 purchase totals = $958.27       $1,058.2156   $1,058.21   $1,058.15   $1,058.30