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	$78.81	4.765%	$82.5653	$82.57	$82.55	$82.60
Purchase #2	$127.30	12.611%	$143.3538	$143.35	$143.35	$143.40
Purchase #3	$118.72	11.309%	$132.146	$132.15	$132.15	$132.10
Purchase #4	$165.29	8.455%	$179.2653	$179.27	$179.25	$179.30
Purchase #5	$235.29	10.262%	$259.4355	$259.44	$259.45	$259.40
Purchase #6	$37.95	11.491%	$42.3108	$42.31	$42.30	$42.30
Purchase #7	$142.92	8.648%	$155.2797	$155.28	$155.30	$155.30
7 purchase totals =	$906.28		$994.3564	$994.37	$994.35	$994.40