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	$89.83	11.862%	$100.4856	$100.49	$100.50	$100.50
Purchase #2	$146.97	6.460%	$156.4643	$156.46	$156.45	$156.50
Purchase #3	$242.60	9.682%	$266.0885	$266.09	$266.10	$266.10
Purchase #4	$201.86	3.685%	$209.2985	$209.30	$209.30	$209.30
Purchase #5	$240.32	11.545%	$268.0649	$268.06	$268.05	$268.10
Purchase #6	$45.25	12.315%	$50.8225	$50.82	$50.80	$50.80
Purchase #7	$213.68	4.353%	$222.9815	$222.98	$223.00	$223.00
7 purchase totals =	$1,180.51		$1,274.2058	$1,274.20	$1,274.20	$1,274.30