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	$136.36	3.472%	$141.0944	$141.09	$141.10	$141.10
Purchase #2	$242.54	10.458%	$267.9048	$267.90	$267.90	$267.90
Purchase #3	$155.32	6.329%	$165.1502	$165.15	$165.15	$165.20
Purchase #4	$189.56	13.210%	$214.6009	$214.60	$214.60	$214.60
Purchase #5	$56.46	10.703%	$62.5029	$62.50	$62.50	$62.50
Purchase #6	$109.64	7.388%	$117.7402	$117.74	$117.75	$117.70
Purchase #7	$45.64	7.146%	$48.9014	$48.90	$48.90	$48.90
7 purchase totals =	$935.52		$1,017.8948	$1,017.88	$1,017.90	$1,017.90