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	$166.33	3.657%	$172.4127	$172.41	$172.40	$172.40
Purchase #2	$90.92	9.448%	$99.5101	$99.51	$99.50	$99.50
Purchase #3	$84.99	8.870%	$92.5286	$92.53	$92.55	$92.50
Purchase #4	$165.91	4.817%	$173.9019	$173.90	$173.90	$173.90
Purchase #5	$58.93	4.656%	$61.6738	$61.67	$61.65	$61.70
Purchase #6	$63.66	11.477%	$70.9663	$70.97	$70.95	$71.00
Purchase #7	$52.76	4.108%	$54.9274	$54.93	$54.95	$54.90
7 purchase totals =	$683.50		$725.9208	$725.92	$725.90	$725.90