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	$197.75	12.538%	$222.5439	$222.54	$222.55	$222.50
Purchase #2	$245.54	4.698%	$257.0755	$257.08	$257.10	$257.10
Purchase #3	$173.29	13.333%	$196.3948	$196.39	$196.40	$196.40
Purchase #4	$137.27	13.690%	$156.0623	$156.06	$156.05	$156.10
Purchase #5	$215.55	3.335%	$222.7386	$222.74	$222.75	$222.70
Purchase #6	$104.35	3.635%	$108.1431	$108.14	$108.15	$108.10
Purchase #7	$71.63	6.275%	$76.1248	$76.12	$76.10	$76.10
7 purchase totals =	$1,145.38		$1,239.0830	$1,239.07	$1,239.10	$1,239.00