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 $136.65   11.349%   $152.1584   $152.16   $152.15   $152.20  
  Purchase #2 $71.60   4.327%   $74.6981   $74.70   $74.70   $74.70  
  Purchase #3 $146.27   13.138%   $165.487   $165.49   $165.50   $165.50  
  Purchase #4 $130.55   8.663%   $141.8595   $141.86   $141.85   $141.90  
  Purchase #5 $78.80   9.589%   $86.3561   $86.36   $86.35   $86.40  
  Purchase #6 $20.27   5.428%   $21.3703   $21.37   $21.35   $21.40  
  Purchase #7 $247.85   6.126%   $263.0333   $263.03   $263.05   $263.00  
  7 purchase totals = $831.99       $904.9627   $904.97   $904.95   $905.10