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	$235.29	6.720%	$251.1015	$251.10	$251.10	$251.10
Purchase #2	$170.47	7.440%	$183.153	$183.15	$183.15	$183.20
Purchase #3	$82.41	8.635%	$89.5261	$89.53	$89.55	$89.50
Purchase #4	$154.81	4.409%	$161.6356	$161.64	$161.65	$161.60
Purchase #5	$199.59	11.439%	$222.4211	$222.42	$222.40	$222.40
Purchase #6	$181.32	13.359%	$205.5425	$205.54	$205.55	$205.50
Purchase #7	$102.57	3.190%	$105.842	$105.84	$105.85	$105.80
7 purchase totals =	$1,126.46		$1,219.2218	$1,219.22	$1,219.25	$1,219.10