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	$45.25	12.308%	$50.8194	$50.82	$50.80	$50.80
Purchase #2	$151.72	4.560%	$158.6384	$158.64	$158.65	$158.60
Purchase #3	$19.39	9.649%	$21.2609	$21.26	$21.25	$21.30
Purchase #4	$140.79	4.572%	$147.2269	$147.23	$147.25	$147.20
Purchase #5	$245.39	5.198%	$258.1454	$258.15	$258.15	$258.10
Purchase #6	$183.94	8.578%	$199.7184	$199.72	$199.70	$199.70
Purchase #7	$230.90	12.220%	$259.116	$259.12	$259.10	$259.10
7 purchase totals =	$1,017.38		$1,094.9254	$1,094.94	$1,094.90	$1,094.80