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	$48.45	12.550%	$54.5305	$54.53	$54.55	$54.50
Purchase #2	$190.54	10.442%	$210.4362	$210.44	$210.45	$210.40
Purchase #3	$170.99	12.530%	$192.415	$192.42	$192.40	$192.40
Purchase #4	$55.89	7.193%	$59.9102	$59.91	$59.90	$59.90
Purchase #5	$17.45	13.848%	$19.8665	$19.87	$19.85	$19.90
Purchase #6	$87.64	13.225%	$99.2304	$99.23	$99.25	$99.20
Purchase #7	$178.77	4.457%	$186.7378	$186.74	$186.75	$186.70
7 purchase totals =	$749.73		$823.1266	$823.14	$823.15	$823.00