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	$35.61	13.751%	$40.5067	$40.51	$40.50	$40.50
Purchase #2	$111.74	5.557%	$117.9494	$117.95	$117.95	$117.90
Purchase #3	$58.69	12.317%	$65.9188	$65.92	$65.90	$65.90
Purchase #4	$103.36	7.811%	$111.4334	$111.43	$111.45	$111.40
Purchase #5	$141.70	4.616%	$148.2409	$148.24	$148.25	$148.20
Purchase #6	$157.80	11.295%	$175.6235	$175.62	$175.60	$175.60
Purchase #7	$64.46	5.399%	$67.9402	$67.94	$67.95	$67.90
7 purchase totals =	$673.36		$727.6129	$727.61	$727.60	$727.40