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	$115.40	11.701%	$128.903	$128.90	$128.90	$128.90
Purchase #2	$197.30	13.584%	$224.1012	$224.10	$224.10	$224.10
Purchase #3	$239.77	4.466%	$250.4781	$250.48	$250.50	$250.50
Purchase #4	$188.29	6.575%	$200.6701	$200.67	$200.65	$200.70
Purchase #5	$135.47	11.333%	$150.8228	$150.82	$150.80	$150.80
Purchase #6	$68.28	5.746%	$72.2034	$72.20	$72.20	$72.20
Purchase #7	$143.67	8.241%	$155.5098	$155.51	$155.50	$155.50
7 purchase totals =	$1,088.18		$1,182.6884	$1,182.68	$1,182.65	$1,182.70