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	$185.95	6.693%	$198.3956	$198.40	$198.40	$198.40
Purchase #2	$122.91	4.241%	$128.1226	$128.12	$128.10	$128.10
Purchase #3	$146.73	6.701%	$156.5624	$156.56	$156.55	$156.60
Purchase #4	$94.94	8.551%	$103.0583	$103.06	$103.05	$103.10
Purchase #5	$52.45	7.698%	$56.4876	$56.49	$56.50	$56.50
Purchase #6	$145.64	6.683%	$155.3731	$155.37	$155.35	$155.40
Purchase #7	$38.45	7.840%	$41.4645	$41.46	$41.45	$41.50
7 purchase totals =	$787.07		$839.4641	$839.46	$839.40	$839.60