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	$226.58	13.860%	$257.984	$257.98	$258.00	$258.00
Purchase #2	$153.60	9.455%	$168.1229	$168.12	$168.10	$168.10
Purchase #3	$131.72	9.342%	$144.0253	$144.03	$144.05	$144.00
Purchase #4	$175.84	5.521%	$185.5481	$185.55	$185.55	$185.50
Purchase #5	$11.92	5.469%	$12.5719	$12.57	$12.55	$12.60
Purchase #6	$82.55	7.683%	$88.8923	$88.89	$88.90	$88.90
Purchase #7	$100.31	10.666%	$111.0091	$111.01	$111.00	$111.00
7 purchase totals =	$882.52		$968.1536	$968.15	$968.15	$968.10