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	$194.70	13.461%	$220.9086	$220.91	$220.90	$220.90
Purchase #2	$120.93	7.337%	$129.8026	$129.80	$129.80	$129.80
Purchase #3	$148.73	3.548%	$154.0069	$154.01	$154.00	$154.00
Purchase #4	$33.60	6.131%	$35.66	$35.66	$35.65	$35.70
Purchase #5	$36.83	9.710%	$40.4062	$40.41	$40.40	$40.40
Purchase #6	$162.50	10.490%	$179.5463	$179.55	$179.55	$179.50
Purchase #7	$78.45	13.618%	$89.1333	$89.13	$89.15	$89.10
7 purchase totals =	$775.74		$849.4639	$849.47	$849.45	$849.40