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	$234.61	12.317%	$263.5069	$263.51	$263.50	$263.50
Purchase #2	$133.49	3.134%	$137.6736	$137.67	$137.65	$137.70
Purchase #3	$49.80	6.519%	$53.0465	$53.05	$53.05	$53.00
Purchase #4	$125.61	10.732%	$139.0905	$139.09	$139.10	$139.10
Purchase #5	$61.54	5.210%	$64.7462	$64.75	$64.75	$64.70
Purchase #6	$99.48	11.755%	$111.1739	$111.17	$111.15	$111.20
Purchase #7	$108.54	5.306%	$114.2991	$114.30	$114.30	$114.30
7 purchase totals =	$813.07		$883.5367	$883.54	$883.50	$883.50