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	$127.84	13.197%	$144.711	$144.71	$144.70	$144.70
Purchase #2	$136.41	4.219%	$142.1651	$142.17	$142.15	$142.20
Purchase #3	$227.57	10.428%	$251.301	$251.30	$251.30	$251.30
Purchase #4	$239.80	7.714%	$258.2982	$258.30	$258.30	$258.30
Purchase #5	$114.60	11.776%	$128.0953	$128.10	$128.10	$128.10
Purchase #6	$157.45	9.583%	$172.5384	$172.54	$172.55	$172.50
Purchase #7	$168.63	9.400%	$184.4812	$184.48	$184.50	$184.50
7 purchase totals =	$1,172.30		$1,281.5902	$1,281.60	$1,281.60	$1,281.60