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	$74.66	11.600%	$83.3206	$83.32	$83.30	$83.30
Purchase #2	$50.47	4.568%	$52.7755	$52.78	$52.80	$52.80
Purchase #3	$167.37	9.863%	$183.8777	$183.88	$183.90	$183.90
Purchase #4	$76.44	7.353%	$82.0606	$82.06	$82.05	$82.10
Purchase #5	$79.52	5.527%	$83.9151	$83.92	$83.90	$83.90
Purchase #6	$104.69	10.365%	$115.5411	$115.54	$115.55	$115.50
Purchase #7	$229.38	5.689%	$242.4294	$242.43	$242.45	$242.40
7 purchase totals =	$782.53		$843.9200	$843.93	$843.95	$843.90