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	$104.70	13.365%	$118.6932	$118.69	$118.70	$118.70
Purchase #2	$40.56	11.576%	$45.2552	$45.26	$45.25	$45.30
Purchase #3	$199.95	4.850%	$209.6476	$209.65	$209.65	$209.60
Purchase #4	$145.77	8.118%	$157.6036	$157.60	$157.60	$157.60
Purchase #5	$28.56	6.498%	$30.4158	$30.42	$30.40	$30.40
Purchase #6	$174.65	12.755%	$196.9266	$196.93	$196.95	$196.90
Purchase #7	$226.72	6.125%	$240.6066	$240.61	$240.60	$240.60
7 purchase totals =	$920.91		$999.1486	$999.16	$999.15	$999.10