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	$73.90	7.359%	$79.3383	$79.34	$79.35	$79.30
Purchase #2	$71.56	9.523%	$78.3747	$78.37	$78.35	$78.40
Purchase #3	$161.42	3.179%	$166.5515	$166.55	$166.55	$166.60
Purchase #4	$176.72	13.243%	$200.123	$200.12	$200.10	$200.10
Purchase #5	$198.30	11.525%	$221.1541	$221.15	$221.15	$221.20
Purchase #6	$176.38	13.150%	$199.574	$199.57	$199.55	$199.60
Purchase #7	$181.39	5.205%	$190.8313	$190.83	$190.85	$190.80
7 purchase totals =	$1,039.67		$1,135.9469	$1,135.93	$1,135.90	$1,136.00