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 $217.91   10.613%   $241.0368   $241.04   $241.05   $241.00  
  Purchase #2 $96.31   10.227%   $106.1596   $106.16   $106.15   $106.20  
  Purchase #3 $55.28   11.325%   $61.5405   $61.54   $61.55   $61.50  
  Purchase #4 $47.34   5.510%   $49.9484   $49.95   $49.95   $49.90  
  Purchase #5 $11.64   9.398%   $12.7339   $12.73   $12.75   $12.70  
  Purchase #6 $53.73   4.141%   $55.955   $55.96   $55.95   $56.00  
  Purchase #7 $168.70   8.681%   $183.3448   $183.34   $183.35   $183.30  
  7 purchase totals = $650.91       $710.7190   $710.72   $710.75   $710.60