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	$115.93	3.863%	$120.4084	$120.41	$120.40	$120.40
Purchase #2	$135.64	6.209%	$144.0619	$144.06	$144.05	$144.10
Purchase #3	$124.33	12.143%	$139.4274	$139.43	$139.45	$139.40
Purchase #4	$220.77	10.650%	$244.282	$244.28	$244.30	$244.30
Purchase #5	$230.25	3.540%	$238.4009	$238.40	$238.40	$238.40
Purchase #6	$130.27	12.285%	$146.2737	$146.27	$146.25	$146.30
Purchase #7	$250.64	6.694%	$267.4178	$267.42	$267.40	$267.40
7 purchase totals =	$1,207.83		$1,300.2721	$1,300.27	$1,300.25	$1,300.30