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	$19.47	10.105%	$21.4374	$21.44	$21.45	$21.40
Purchase #2	$155.81	7.109%	$166.8865	$166.89	$166.90	$166.90
Purchase #3	$36.33	6.541%	$38.7063	$38.71	$38.70	$38.70
Purchase #4	$179.89	6.244%	$191.1223	$191.12	$191.10	$191.10
Purchase #5	$170.80	3.300%	$176.4364	$176.44	$176.45	$176.40
Purchase #6	$21.82	3.387%	$22.559	$22.56	$22.55	$22.60
Purchase #7	$130.38	7.572%	$140.2524	$140.25	$140.25	$140.30
7 purchase totals =	$714.50		$757.4003	$757.41	$757.40	$757.40