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	$48.39	5.616%	$51.1076	$51.11	$51.10	$51.10
Purchase #2	$118.59	12.753%	$133.7138	$133.71	$133.70	$133.70
Purchase #3	$178.56	9.431%	$195.4	$195.40	$195.40	$195.40
Purchase #4	$196.38	4.868%	$205.9398	$205.94	$205.95	$205.90
Purchase #5	$128.54	8.702%	$139.7256	$139.73	$139.75	$139.70
Purchase #6	$99.79	11.526%	$111.2918	$111.29	$111.30	$111.30
Purchase #7	$75.57	8.575%	$82.0501	$82.05	$82.05	$82.10
7 purchase totals =	$845.82		$919.2287	$919.23	$919.25	$919.20