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 $204.49   8.196%   $221.25   $221.25   $221.25   $221.30  
  Purchase #2 $7.75   7.837%   $8.3574   $8.36   $8.35   $8.40  
  Purchase #3 $40.69   8.197%   $44.0254   $44.03   $44.05   $44.00  
  Purchase #4 $234.48   7.848%   $252.882   $252.88   $252.90   $252.90  
  Purchase #5 $127.97   5.163%   $134.5771   $134.58   $134.60   $134.60  
  Purchase #6 $157.78   4.708%   $165.2083   $165.21   $165.20   $165.20  
  Purchase #7 $83.28   9.600%   $91.2749   $91.27   $91.25   $91.30  
  7 purchase totals = $856.44       $917.5751   $917.58   $917.60   $917.70