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	$171.81	12.413%	$193.1368	$193.14	$193.15	$193.10
Purchase #2	$132.66	8.108%	$143.4161	$143.42	$143.40	$143.40
Purchase #3	$132.76	13.389%	$150.5352	$150.54	$150.55	$150.50
Purchase #4	$25.57	11.154%	$28.4221	$28.42	$28.40	$28.40
Purchase #5	$53.38	5.418%	$56.2721	$56.27	$56.25	$56.30
Purchase #6	$179.62	5.759%	$189.9643	$189.96	$189.95	$190.00
Purchase #7	$47.59	11.687%	$53.1518	$53.15	$53.15	$53.20
7 purchase totals =	$743.39		$814.8984	$814.90	$814.85	$814.90