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	$61.30	9.363%	$67.0395	$67.04	$67.05	$67.00
Purchase #2	$20.75	6.406%	$22.0792	$22.08	$22.10	$22.10
Purchase #3	$158.31	8.168%	$171.2408	$171.24	$171.25	$171.20
Purchase #4	$38.69	10.313%	$42.6801	$42.68	$42.70	$42.70
Purchase #5	$207.49	12.552%	$233.5341	$233.53	$233.55	$233.50
Purchase #6	$134.37	12.793%	$151.56	$151.56	$151.55	$151.60
Purchase #7	$132.89	7.406%	$142.7318	$142.73	$142.75	$142.70
7 purchase totals =	$753.80		$830.8655	$830.86	$830.95	$830.80