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	$50.26	12.776%	$56.6812	$56.68	$56.70	$56.70
Purchase #2	$174.88	12.144%	$196.1174	$196.12	$196.10	$196.10
Purchase #3	$210.70	5.448%	$222.1789	$222.18	$222.20	$222.20
Purchase #4	$58.84	9.250%	$64.2827	$64.28	$64.30	$64.30
Purchase #5	$77.98	5.464%	$82.2408	$82.24	$82.25	$82.20
Purchase #6	$118.81	4.605%	$124.2812	$124.28	$124.30	$124.30
Purchase #7	$223.75	4.180%	$233.1028	$233.10	$233.10	$233.10
7 purchase totals =	$915.22		$978.8850	$978.88	$978.95	$978.90