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	$27.54	5.296%	$28.9985	$29.00	$29.00	$29.00
Purchase #2	$89.53	11.694%	$99.9996	$100.00	$100.00	$100.00
Purchase #3	$244.43	8.396%	$264.9523	$264.95	$264.95	$265.00
Purchase #4	$53.45	6.482%	$56.9146	$56.91	$56.90	$56.90
Purchase #5	$140.42	4.281%	$146.4314	$146.43	$146.45	$146.40
Purchase #6	$227.75	12.357%	$255.8931	$255.89	$255.90	$255.90
Purchase #7	$244.42	10.497%	$270.0768	$270.08	$270.10	$270.10
7 purchase totals =	$1,027.54		$1,123.2663	$1,123.26	$1,123.30	$1,123.30