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	$135.49	9.259%	$148.035	$148.04	$148.05	$148.00
Purchase #2	$47.33	7.574%	$50.9148	$50.91	$50.90	$50.90
Purchase #3	$145.31	6.234%	$154.3686	$154.37	$154.35	$154.40
Purchase #4	$89.67	10.729%	$99.2907	$99.29	$99.30	$99.30
Purchase #5	$60.93	9.353%	$66.6288	$66.63	$66.65	$66.60
Purchase #6	$40.25	3.200%	$41.538	$41.54	$41.55	$41.50
Purchase #7	$73.71	7.208%	$79.023	$79.02	$79.00	$79.00
7 purchase totals =	$592.69		$639.7989	$639.80	$639.80	$639.70