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	$6.71	6.113%	$7.1202	$7.12	$7.10	$7.10
Purchase #2	$49.86	8.868%	$54.2816	$54.28	$54.30	$54.30
Purchase #3	$142.45	4.801%	$149.289	$149.29	$149.30	$149.30
Purchase #4	$94.45	7.478%	$101.513	$101.51	$101.50	$101.50
Purchase #5	$101.86	9.693%	$111.7333	$111.73	$111.75	$111.70
Purchase #6	$152.48	6.844%	$162.9157	$162.92	$162.90	$162.90
Purchase #7	$23.38	7.450%	$25.1218	$25.12	$25.10	$25.10
7 purchase totals =	$571.19		$611.9746	$611.97	$611.95	$611.90