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	$79.54	13.405%	$90.2023	$90.20	$90.20	$90.20
Purchase #2	$221.43	9.507%	$242.4814	$242.48	$242.50	$242.50
Purchase #3	$145.28	4.244%	$151.4457	$151.45	$151.45	$151.40
Purchase #4	$51.32	12.676%	$57.8253	$57.83	$57.85	$57.80
Purchase #5	$105.37	12.741%	$118.7952	$118.80	$118.80	$118.80
Purchase #6	$190.77	9.331%	$208.5707	$208.57	$208.55	$208.60
Purchase #7	$13.75	11.142%	$15.282	$15.28	$15.30	$15.30
7 purchase totals =	$807.46		$884.6026	$884.61	$884.65	$884.60