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	$23.72	6.114%	$25.1702	$25.17	$25.15	$25.20
Purchase #2	$201.83	4.704%	$211.3241	$211.32	$211.30	$211.30
Purchase #3	$44.89	13.467%	$50.9353	$50.94	$50.95	$50.90
Purchase #4	$88.63	8.160%	$95.8622	$95.86	$95.85	$95.90
Purchase #5	$142.32	13.302%	$161.2514	$161.25	$161.25	$161.30
Purchase #6	$175.73	11.599%	$196.1129	$196.11	$196.10	$196.10
Purchase #7	$149.49	5.114%	$157.1349	$157.13	$157.15	$157.10
7 purchase totals =	$826.61		$897.7910	$897.78	$897.75	$897.80