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	$20.88	4.656%	$21.8522	$21.85	$21.85	$21.90
Purchase #2	$41.44	8.161%	$44.8219	$44.82	$44.80	$44.80
Purchase #3	$103.80	7.616%	$111.7054	$111.71	$111.70	$111.70
Purchase #4	$57.33	8.614%	$62.2684	$62.27	$62.25	$62.30
Purchase #5	$121.70	9.478%	$133.2347	$133.23	$133.25	$133.20
Purchase #6	$45.97	5.394%	$48.4496	$48.45	$48.45	$48.40
Purchase #7	$181.30	9.851%	$199.1599	$199.16	$199.15	$199.20
7 purchase totals =	$572.42		$621.4921	$621.49	$621.45	$621.50