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	$128.83	6.281%	$136.9218	$136.92	$136.90	$136.90
Purchase #2	$199.98	11.822%	$223.6216	$223.62	$223.60	$223.60
Purchase #3	$94.40	9.205%	$103.0895	$103.09	$103.10	$103.10
Purchase #4	$218.41	13.278%	$247.4105	$247.41	$247.40	$247.40
Purchase #5	$17.95	7.335%	$19.2666	$19.27	$19.25	$19.30
Purchase #6	$194.72	8.533%	$211.3355	$211.34	$211.35	$211.30
Purchase #7	$148.82	6.438%	$158.401	$158.40	$158.40	$158.40
7 purchase totals =	$1,003.11		$1,100.0465	$1,100.05	$1,100.00	$1,100.00