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	$18.59	9.338%	$20.3259	$20.33	$20.35	$20.30
Purchase #2	$92.57	13.553%	$105.116	$105.12	$105.10	$105.10
Purchase #3	$53.87	9.411%	$58.9397	$58.94	$58.95	$58.90
Purchase #4	$145.74	3.424%	$150.7301	$150.73	$150.75	$150.70
Purchase #5	$172.76	3.111%	$178.1346	$178.13	$178.15	$178.10
Purchase #6	$191.94	9.672%	$210.5044	$210.50	$210.50	$210.50
Purchase #7	$128.68	11.752%	$143.8025	$143.80	$143.80	$143.80
7 purchase totals =	$804.15		$867.5532	$867.55	$867.60	$867.40