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	$96.78	3.644%	$100.3067	$100.31	$100.30	$100.30
Purchase #2	$181.83	7.792%	$195.9982	$196.00	$196.00	$196.00
Purchase #3	$188.97	8.288%	$204.6318	$204.63	$204.65	$204.60
Purchase #4	$117.88	8.452%	$127.8432	$127.84	$127.85	$127.80
Purchase #5	$211.70	3.282%	$218.648	$218.65	$218.65	$218.60
Purchase #6	$127.25	6.158%	$135.0861	$135.09	$135.10	$135.10
Purchase #7	$64.87	12.433%	$72.9353	$72.94	$72.95	$72.90
7 purchase totals =	$989.28		$1,055.4493	$1,055.46	$1,055.50	$1,055.30