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 $109.67   8.820%   $119.3429   $119.34   $119.35   $119.30  
  Purchase #2 $199.83   4.508%   $208.8383   $208.84   $208.85   $208.80  
  Purchase #3 $100.58   11.621%   $112.2684   $112.27   $112.25   $112.30  
  Purchase #4 $232.79   8.645%   $252.9147   $252.91   $252.90   $252.90  
  Purchase #5 $133.28   7.463%   $143.2267   $143.23   $143.25   $143.20  
  Purchase #6 $132.82   6.617%   $141.6087   $141.61   $141.60   $141.60  
  Purchase #7 $231.67   6.288%   $246.2374   $246.24   $246.25   $246.20  
  7 purchase totals = $1,140.64       $1,224.4371   $1,224.44   $1,224.45   $1,224.30