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	$161.91	10.853%	$179.4821	$179.48	$179.50	$179.50
Purchase #2	$127.69	11.868%	$142.8442	$142.84	$142.85	$142.80
Purchase #3	$106.30	4.488%	$111.0707	$111.07	$111.05	$111.10
Purchase #4	$60.97	11.636%	$68.0645	$68.06	$68.05	$68.10
Purchase #5	$94.69	3.680%	$98.1746	$98.17	$98.15	$98.20
Purchase #6	$62.91	6.334%	$66.8947	$66.89	$66.90	$66.90
Purchase #7	$154.69	3.545%	$160.1738	$160.17	$160.15	$160.20
7 purchase totals =	$769.16		$826.7046	$826.68	$826.65	$826.80