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	$78.46	6.594%	$83.6337	$83.63	$83.65	$83.60
Purchase #2	$145.36	6.155%	$154.3069	$154.31	$154.30	$154.30
Purchase #3	$72.81	9.263%	$79.5544	$79.55	$79.55	$79.60
Purchase #4	$132.99	13.638%	$151.1272	$151.13	$151.15	$151.10
Purchase #5	$57.47	5.735%	$60.7659	$60.77	$60.75	$60.80
Purchase #6	$246.28	3.826%	$255.7027	$255.70	$255.70	$255.70
Purchase #7	$52.94	13.205%	$59.9307	$59.93	$59.95	$59.90
7 purchase totals =	$786.31		$845.0215	$845.02	$845.05	$845.00