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	$106.28	7.164%	$113.8939	$113.89	$113.90	$113.90
Purchase #2	$189.97	10.246%	$209.4343	$209.43	$209.45	$209.40
Purchase #3	$100.29	5.663%	$105.9694	$105.97	$105.95	$106.00
Purchase #4	$89.83	11.859%	$100.4829	$100.48	$100.50	$100.50
Purchase #5	$164.74	12.190%	$184.8218	$184.82	$184.80	$184.80
Purchase #6	$82.89	3.823%	$86.0589	$86.06	$86.05	$86.10
Purchase #7	$79.28	4.252%	$82.651	$82.65	$82.65	$82.70
7 purchase totals =	$813.28		$883.3122	$883.30	$883.30	$883.40