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	$39.44	10.851%	$43.7196	$43.72	$43.70	$43.70
Purchase #2	$82.36	7.347%	$88.411	$88.41	$88.40	$88.40
Purchase #3	$180.55	5.285%	$190.0921	$190.09	$190.10	$190.10
Purchase #4	$54.78	5.749%	$57.9293	$57.93	$57.95	$57.90
Purchase #5	$59.58	4.514%	$62.2694	$62.27	$62.25	$62.30
Purchase #6	$183.72	5.267%	$193.3965	$193.40	$193.40	$193.40
Purchase #7	$142.90	11.164%	$158.8534	$158.85	$158.85	$158.90
7 purchase totals =	$743.33		$794.6713	$794.67	$794.65	$794.70