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	$248.48	13.553%	$282.1565	$282.16	$282.15	$282.20
Purchase #2	$101.91	6.650%	$108.687	$108.69	$108.70	$108.70
Purchase #3	$152.86	12.291%	$171.648	$171.65	$171.65	$171.60
Purchase #4	$91.25	11.128%	$101.4043	$101.40	$101.40	$101.40
Purchase #5	$138.61	3.465%	$143.4128	$143.41	$143.40	$143.40
Purchase #6	$38.64	11.593%	$43.1195	$43.12	$43.10	$43.10
Purchase #7	$234.47	6.652%	$250.0669	$250.07	$250.05	$250.10
7 purchase totals =	$1,006.22		$1,100.4950	$1,100.50	$1,100.45	$1,100.50