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	$127.31	12.645%	$143.4083	$143.41	$143.40	$143.40
Purchase #2	$178.27	13.433%	$202.217	$202.22	$202.20	$202.20
Purchase #3	$56.57	5.826%	$59.8658	$59.87	$59.85	$59.90
Purchase #4	$162.35	6.412%	$172.7599	$172.76	$172.75	$172.80
Purchase #5	$172.72	13.746%	$196.4621	$196.46	$196.45	$196.50
Purchase #6	$115.63	13.472%	$131.2077	$131.21	$131.20	$131.20
Purchase #7	$49.54	8.419%	$53.7108	$53.71	$53.70	$53.70
7 purchase totals =	$862.39		$959.6316	$959.64	$959.55	$959.70