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	$151.87	3.196%	$156.7238	$156.72	$156.70	$156.70
Purchase #2	$199.82	6.388%	$212.5845	$212.58	$212.60	$212.60
Purchase #3	$120.33	9.171%	$131.3655	$131.37	$131.35	$131.40
Purchase #4	$160.26	12.851%	$180.855	$180.86	$180.85	$180.90
Purchase #5	$128.82	9.547%	$141.1184	$141.12	$141.10	$141.10
Purchase #6	$56.53	10.450%	$62.4374	$62.44	$62.45	$62.40
Purchase #7	$40.82	8.817%	$44.4191	$44.42	$44.40	$44.40
7 purchase totals =	$858.45		$929.5037	$929.51	$929.45	$929.50