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	$83.32	5.494%	$87.8976	$87.90	$87.90	$87.90
Purchase #2	$82.90	8.601%	$90.0302	$90.03	$90.05	$90.00
Purchase #3	$190.89	10.730%	$211.3725	$211.37	$211.35	$211.40
Purchase #4	$189.59	8.479%	$205.6653	$205.67	$205.65	$205.70
Purchase #5	$13.33	3.743%	$13.8289	$13.83	$13.85	$13.80
Purchase #6	$5.62	11.794%	$6.2828	$6.28	$6.30	$6.30
Purchase #7	$52.56	9.772%	$57.6962	$57.70	$57.70	$57.70
7 purchase totals =	$618.21		$672.7735	$672.78	$672.80	$672.80