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	$19.64	5.734%	$20.7662	$20.77	$20.75	$20.80
Purchase #2	$99.39	13.726%	$113.0323	$113.03	$113.05	$113.00
Purchase #3	$9.34	11.392%	$10.404	$10.40	$10.40	$10.40
Purchase #4	$9.38	13.216%	$10.6197	$10.62	$10.60	$10.60
Purchase #5	$173.97	9.737%	$190.9095	$190.91	$190.90	$190.90
Purchase #6	$137.66	13.236%	$155.8807	$155.88	$155.90	$155.90
Purchase #7	$167.72	4.140%	$174.6636	$174.66	$174.65	$174.70
7 purchase totals =	$617.10		$676.2760	$676.27	$676.25	$676.30