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	$74.92	7.109%	$80.2461	$80.25	$80.25	$80.20
Purchase #2	$114.42	3.735%	$118.6936	$118.69	$118.70	$118.70
Purchase #3	$55.89	6.843%	$59.7146	$59.71	$59.70	$59.70
Purchase #4	$123.83	5.646%	$130.8214	$130.82	$130.80	$130.80
Purchase #5	$185.83	10.287%	$204.9463	$204.95	$204.95	$204.90
Purchase #6	$39.93	6.123%	$42.3749	$42.37	$42.35	$42.40
Purchase #7	$169.38	7.679%	$182.3867	$182.39	$182.40	$182.40
7 purchase totals =	$764.20		$819.1836	$819.18	$819.15	$819.10