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	$208.76	6.840%	$223.0392	$223.04	$223.05	$223.00
Purchase #2	$48.75	10.738%	$53.9848	$53.98	$54.00	$54.00
Purchase #3	$178.71	3.343%	$184.6843	$184.68	$184.70	$184.70
Purchase #4	$87.82	4.245%	$91.548	$91.55	$91.55	$91.50
Purchase #5	$18.72	4.418%	$19.547	$19.55	$19.55	$19.50
Purchase #6	$48.65	12.868%	$54.9103	$54.91	$54.90	$54.90
Purchase #7	$120.89	9.653%	$132.5595	$132.56	$132.55	$132.60
7 purchase totals =	$712.30		$760.2731	$760.27	$760.30	$760.20