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	$17.65	10.531%	$19.5087	$19.51	$19.50	$19.50
Purchase #2	$73.48	6.555%	$78.2966	$78.30	$78.30	$78.30
Purchase #3	$120.74	9.250%	$131.9085	$131.91	$131.90	$131.90
Purchase #4	$78.91	11.627%	$88.0849	$88.08	$88.10	$88.10
Purchase #5	$104.86	3.468%	$108.4965	$108.50	$108.50	$108.50
Purchase #6	$144.83	7.128%	$155.1535	$155.15	$155.15	$155.20
Purchase #7	$8.74	12.153%	$9.8022	$9.80	$9.80	$9.80
7 purchase totals =	$549.21		$591.2509	$591.25	$591.25	$591.30