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	$242.63	11.273%	$269.9817	$269.98	$270.00	$270.00
Purchase #2	$85.83	7.516%	$92.281	$92.28	$92.30	$92.30
Purchase #3	$56.52	5.750%	$59.7699	$59.77	$59.75	$59.80
Purchase #4	$57.51	6.225%	$61.09	$61.09	$61.10	$61.10
Purchase #5	$96.35	4.552%	$100.7359	$100.74	$100.75	$100.70
Purchase #6	$50.81	8.804%	$55.2833	$55.28	$55.30	$55.30
Purchase #7	$110.29	11.688%	$123.1807	$123.18	$123.20	$123.20
7 purchase totals =	$699.94		$762.3225	$762.32	$762.40	$762.40