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	$70.26	4.606%	$73.4962	$73.50	$73.50	$73.50
Purchase #2	$51.36	3.446%	$53.1299	$53.13	$53.15	$53.10
Purchase #3	$231.45	13.597%	$262.9203	$262.92	$262.90	$262.90
Purchase #4	$105.92	5.485%	$111.7297	$111.73	$111.75	$111.70
Purchase #5	$82.47	7.739%	$88.8524	$88.85	$88.85	$88.90
Purchase #6	$98.66	4.294%	$102.8965	$102.90	$102.90	$102.90
Purchase #7	$75.67	4.768%	$79.2779	$79.28	$79.30	$79.30
7 purchase totals =	$715.79		$772.3029	$772.31	$772.35	$772.30