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	$100.48	5.735%	$106.2425	$106.24	$106.25	$106.20
Purchase #2	$188.92	5.610%	$199.5184	$199.52	$199.50	$199.50
Purchase #3	$98.36	13.526%	$111.6642	$111.66	$111.65	$111.70
Purchase #4	$79.84	5.116%	$83.9246	$83.92	$83.90	$83.90
Purchase #5	$141.31	10.849%	$156.6407	$156.64	$156.65	$156.60
Purchase #6	$75.51	5.763%	$79.8616	$79.86	$79.85	$79.90
Purchase #7	$213.55	4.381%	$222.9056	$222.91	$222.90	$222.90
7 purchase totals =	$897.97		$960.7576	$960.75	$960.70	$960.70