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	$13.76	13.154%	$15.57	$15.57	$15.55	$15.60
Purchase #2	$235.31	3.235%	$242.9223	$242.92	$242.90	$242.90
Purchase #3	$159.93	5.168%	$168.1952	$168.20	$168.20	$168.20
Purchase #4	$75.28	13.656%	$85.5602	$85.56	$85.55	$85.60
Purchase #5	$129.67	3.743%	$134.5235	$134.52	$134.50	$134.50
Purchase #6	$59.30	5.466%	$62.5413	$62.54	$62.55	$62.50
Purchase #7	$114.63	10.772%	$126.9779	$126.98	$127.00	$127.00
7 purchase totals =	$787.88		$836.2904	$836.29	$836.25	$836.30