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	$117.88	4.792%	$123.5288	$123.53	$123.55	$123.50
Purchase #2	$109.98	9.713%	$120.6624	$120.66	$120.65	$120.70
Purchase #3	$246.91	12.519%	$277.8207	$277.82	$277.80	$277.80
Purchase #4	$246.93	4.614%	$258.3234	$258.32	$258.30	$258.30
Purchase #5	$239.75	13.793%	$272.8187	$272.82	$272.80	$272.80
Purchase #6	$100.42	11.276%	$111.7434	$111.74	$111.75	$111.70
Purchase #7	$114.81	10.645%	$127.0315	$127.03	$127.05	$127.00
7 purchase totals =	$1,176.68		$1,291.9289	$1,291.92	$1,291.90	$1,291.80