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	$74.30	5.672%	$78.5143	$78.51	$78.50	$78.50
Purchase #2	$109.36	7.148%	$117.1771	$117.18	$117.20	$117.20
Purchase #3	$154.84	7.468%	$166.4035	$166.40	$166.40	$166.40
Purchase #4	$157.89	7.432%	$169.6244	$169.62	$169.60	$169.60
Purchase #5	$138.95	4.129%	$144.6872	$144.69	$144.70	$144.70
Purchase #6	$89.75	11.337%	$99.925	$99.93	$99.95	$99.90
Purchase #7	$194.55	11.635%	$217.1859	$217.19	$217.20	$217.20
7 purchase totals =	$919.64		$993.5174	$993.52	$993.55	$993.50