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	$137.80	10.415%	$152.1519	$152.15	$152.15	$152.20
Purchase #2	$165.59	4.131%	$172.4305	$172.43	$172.45	$172.40
Purchase #3	$59.54	10.118%	$65.5643	$65.56	$65.55	$65.60
Purchase #4	$192.64	13.645%	$218.9257	$218.93	$218.95	$218.90
Purchase #5	$170.90	11.230%	$190.0921	$190.09	$190.10	$190.10
Purchase #6	$19.31	4.376%	$20.155	$20.16	$20.15	$20.20
Purchase #7	$92.92	9.697%	$101.9305	$101.93	$101.95	$101.90
7 purchase totals =	$838.70		$921.2500	$921.25	$921.30	$921.30