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	$215.37	3.548%	$223.0113	$223.01	$223.00	$223.00
Purchase #2	$36.68	11.539%	$40.9125	$40.91	$40.90	$40.90
Purchase #3	$107.89	6.488%	$114.8899	$114.89	$114.90	$114.90
Purchase #4	$63.60	4.614%	$66.5345	$66.53	$66.55	$66.50
Purchase #5	$241.74	12.158%	$271.1307	$271.13	$271.15	$271.10
Purchase #6	$39.36	8.690%	$42.7804	$42.78	$42.80	$42.80
Purchase #7	$48.80	9.693%	$53.5302	$53.53	$53.55	$53.50
7 purchase totals =	$753.44		$812.7895	$812.78	$812.85	$812.70