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	$79.71	11.780%	$89.0998	$89.10	$89.10	$89.10
Purchase #2	$245.49	5.436%	$258.8348	$258.83	$258.85	$258.80
Purchase #3	$143.87	11.751%	$160.7762	$160.78	$160.80	$160.80
Purchase #4	$186.32	5.606%	$196.7651	$196.77	$196.75	$196.80
Purchase #5	$60.76	7.799%	$65.4987	$65.50	$65.50	$65.50
Purchase #6	$110.57	11.187%	$122.9395	$122.94	$122.95	$122.90
Purchase #7	$40.27	9.832%	$44.2293	$44.23	$44.25	$44.20
7 purchase totals =	$866.99		$938.1434	$938.15	$938.20	$938.10