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	$228.95	8.272%	$247.8887	$247.89	$247.90	$247.90
Purchase #2	$53.79	13.656%	$61.1356	$61.14	$61.15	$61.10
Purchase #3	$74.74	10.729%	$82.7589	$82.76	$82.75	$82.80
Purchase #4	$175.42	8.215%	$189.8308	$189.83	$189.85	$189.80
Purchase #5	$25.83	12.225%	$28.9877	$28.99	$29.00	$29.00
Purchase #6	$89.58	11.812%	$100.1612	$100.16	$100.15	$100.20
Purchase #7	$62.27	6.330%	$66.2117	$66.21	$66.20	$66.20
7 purchase totals =	$710.58		$776.9746	$776.98	$777.00	$777.00