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	$29.48	6.823%	$31.4914	$31.49	$31.50	$31.50
Purchase #2	$49.90	9.437%	$54.6091	$54.61	$54.60	$54.60
Purchase #3	$163.84	6.152%	$173.9194	$173.92	$173.90	$173.90
Purchase #4	$124.38	8.332%	$134.7433	$134.74	$134.75	$134.70
Purchase #5	$183.28	7.180%	$196.4395	$196.44	$196.45	$196.40
Purchase #6	$223.85	13.709%	$254.5376	$254.54	$254.55	$254.50
Purchase #7	$55.73	6.440%	$59.319	$59.32	$59.30	$59.30
7 purchase totals =	$830.46		$905.0593	$905.06	$905.05	$904.90