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	$237.71	5.588%	$250.9932	$250.99	$251.00	$251.00
Purchase #2	$112.74	11.624%	$125.8449	$125.84	$125.85	$125.80
Purchase #3	$47.32	12.565%	$53.2658	$53.27	$53.25	$53.30
Purchase #4	$69.36	4.317%	$72.3543	$72.35	$72.35	$72.40
Purchase #5	$10.95	13.210%	$12.3965	$12.40	$12.40	$12.40
Purchase #6	$189.71	11.265%	$211.0808	$211.08	$211.10	$211.10
Purchase #7	$83.39	7.376%	$89.5408	$89.54	$89.55	$89.50
7 purchase totals =	$751.18		$815.4763	$815.47	$815.50	$815.50