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	$37.50	9.542%	$41.0783	$41.08	$41.10	$41.10
Purchase #2	$113.38	5.377%	$119.4764	$119.48	$119.50	$119.50
Purchase #3	$171.36	7.128%	$183.5745	$183.57	$183.55	$183.60
Purchase #4	$91.40	9.417%	$100.0071	$100.01	$100.00	$100.00
Purchase #5	$51.28	12.574%	$57.7279	$57.73	$57.75	$57.70
Purchase #6	$232.35	12.797%	$262.0838	$262.08	$262.10	$262.10
Purchase #7	$178.48	10.116%	$196.535	$196.54	$196.55	$196.50
7 purchase totals =	$875.75		$960.4830	$960.49	$960.55	$960.50