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	$32.93	13.848%	$37.4901	$37.49	$37.50	$37.50
Purchase #2	$208.76	9.604%	$228.8093	$228.81	$228.80	$228.80
Purchase #3	$141.93	12.430%	$159.5719	$159.57	$159.55	$159.60
Purchase #4	$239.38	11.565%	$267.0643	$267.06	$267.05	$267.10
Purchase #5	$94.50	11.613%	$105.4743	$105.47	$105.45	$105.50
Purchase #6	$56.72	5.157%	$59.6451	$59.65	$59.65	$59.60
Purchase #7	$44.63	3.294%	$46.1001	$46.10	$46.10	$46.10
7 purchase totals =	$818.85		$904.1551	$904.15	$904.10	$904.20