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	$96.92	12.613%	$109.1445	$109.14	$109.15	$109.10
Purchase #2	$107.87	10.157%	$118.8264	$118.83	$118.85	$118.80
Purchase #3	$216.71	10.560%	$239.5946	$239.59	$239.60	$239.60
Purchase #4	$190.56	8.831%	$207.3884	$207.39	$207.40	$207.40
Purchase #5	$119.90	4.111%	$124.8291	$124.83	$124.85	$124.80
Purchase #6	$115.27	13.560%	$130.9006	$130.90	$130.90	$130.90
Purchase #7	$156.66	7.603%	$168.5709	$168.57	$168.55	$168.60
7 purchase totals =	$1,003.89		$1,099.2545	$1,099.25	$1,099.30	$1,099.20