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	$94.96	6.473%	$101.1068	$101.11	$101.10	$101.10
Purchase #2	$249.86	12.180%	$280.2929	$280.29	$280.30	$280.30
Purchase #3	$51.36	4.533%	$53.6881	$53.69	$53.70	$53.70
Purchase #4	$96.84	3.584%	$100.3107	$100.31	$100.30	$100.30
Purchase #5	$197.46	6.318%	$209.9355	$209.94	$209.95	$209.90
Purchase #6	$30.46	13.659%	$34.6205	$34.62	$34.60	$34.60
Purchase #7	$94.83	10.328%	$104.624	$104.62	$104.60	$104.60
7 purchase totals =	$815.77		$884.5785	$884.58	$884.55	$884.50