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	$75.29	7.132%	$80.6597	$80.66	$80.65	$80.70
Purchase #2	$31.29	6.487%	$33.3198	$33.32	$33.30	$33.30
Purchase #3	$208.66	11.810%	$233.3027	$233.30	$233.30	$233.30
Purchase #4	$25.79	8.442%	$27.9672	$27.97	$27.95	$28.00
Purchase #5	$107.62	3.854%	$111.7677	$111.77	$111.75	$111.80
Purchase #6	$145.43	9.163%	$158.7558	$158.76	$158.75	$158.80
Purchase #7	$141.74	6.345%	$150.7334	$150.73	$150.75	$150.70
7 purchase totals =	$735.82		$796.5063	$796.51	$796.45	$796.60