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	$77.35	4.155%	$80.5639	$80.56	$80.55	$80.60
Purchase #2	$145.64	10.460%	$160.8739	$160.87	$160.85	$160.90
Purchase #3	$158.86	9.113%	$173.3369	$173.34	$173.35	$173.30
Purchase #4	$34.84	8.604%	$37.8376	$37.84	$37.85	$37.80
Purchase #5	$226.44	8.318%	$245.2753	$245.28	$245.30	$245.30
Purchase #6	$133.82	6.594%	$142.6441	$142.64	$142.65	$142.60
Purchase #7	$35.93	13.736%	$40.8653	$40.87	$40.85	$40.90
7 purchase totals =	$812.88		$881.3970	$881.40	$881.40	$881.40