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	$19.82	8.284%	$21.4619	$21.46	$21.45	$21.50
Purchase #2	$82.57	8.843%	$89.8717	$89.87	$89.85	$89.90
Purchase #3	$97.37	11.184%	$108.2599	$108.26	$108.25	$108.30
Purchase #4	$168.48	3.540%	$174.4442	$174.44	$174.45	$174.40
Purchase #5	$147.65	7.735%	$159.0707	$159.07	$159.05	$159.10
Purchase #6	$133.40	11.494%	$148.733	$148.73	$148.75	$148.70
Purchase #7	$139.45	9.426%	$152.5946	$152.59	$152.60	$152.60
7 purchase totals =	$788.74		$854.4360	$854.42	$854.40	$854.50