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	$19.63	9.581%	$21.5108	$21.51	$21.50	$21.50
Purchase #2	$184.47	8.379%	$199.9267	$199.93	$199.95	$199.90
Purchase #3	$149.66	8.620%	$162.5607	$162.56	$162.55	$162.60
Purchase #4	$191.83	12.346%	$215.5133	$215.51	$215.50	$215.50
Purchase #5	$235.53	8.712%	$256.0494	$256.05	$256.05	$256.00
Purchase #6	$147.95	6.727%	$157.9026	$157.90	$157.90	$157.90
Purchase #7	$121.87	4.707%	$127.6064	$127.61	$127.60	$127.60
7 purchase totals =	$1,050.94		$1,141.0699	$1,141.07	$1,141.05	$1,141.00