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	$246.41	3.280%	$254.4922	$254.49	$254.50	$254.50
Purchase #2	$136.55	4.375%	$142.5241	$142.52	$142.50	$142.50
Purchase #3	$73.86	12.344%	$82.9773	$82.98	$83.00	$83.00
Purchase #4	$17.25	4.397%	$18.0085	$18.01	$18.00	$18.00
Purchase #5	$91.67	9.231%	$100.1321	$100.13	$100.15	$100.10
Purchase #6	$206.56	3.869%	$214.5518	$214.55	$214.55	$214.60
Purchase #7	$11.40	12.589%	$12.8351	$12.84	$12.85	$12.80
7 purchase totals =	$783.70		$825.5211	$825.52	$825.55	$825.50