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	$75.63	3.357%	$78.1689	$78.17	$78.15	$78.20
Purchase #2	$70.83	11.306%	$78.838	$78.84	$78.85	$78.80
Purchase #3	$146.62	13.446%	$166.3345	$166.33	$166.35	$166.30
Purchase #4	$222.45	9.621%	$243.8519	$243.85	$243.85	$243.90
Purchase #5	$9.76	10.478%	$10.7827	$10.78	$10.80	$10.80
Purchase #6	$19.55	12.332%	$21.9609	$21.96	$21.95	$22.00
Purchase #7	$215.35	13.458%	$244.3318	$244.33	$244.35	$244.30
7 purchase totals =	$760.19		$844.2687	$844.26	$844.30	$844.30