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	$109.71	5.752%	$116.0205	$116.02	$116.00	$116.00
Purchase #2	$118.45	11.395%	$131.9474	$131.95	$131.95	$131.90
Purchase #3	$173.59	10.131%	$191.1764	$191.18	$191.20	$191.20
Purchase #4	$28.25	4.438%	$29.5037	$29.50	$29.50	$29.50
Purchase #5	$16.27	13.635%	$18.4884	$18.49	$18.50	$18.50
Purchase #6	$199.92	4.830%	$209.5761	$209.58	$209.60	$209.60
Purchase #7	$128.61	12.400%	$144.5576	$144.56	$144.55	$144.60
7 purchase totals =	$774.80		$841.2701	$841.28	$841.30	$841.30