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	$128.55	10.178%	$141.6338	$141.63	$141.65	$141.60
Purchase #2	$122.79	7.322%	$131.7807	$131.78	$131.80	$131.80
Purchase #3	$89.66	12.809%	$101.1445	$101.14	$101.15	$101.10
Purchase #4	$185.30	9.259%	$202.4569	$202.46	$202.45	$202.50
Purchase #5	$71.27	10.412%	$78.6906	$78.69	$78.70	$78.70
Purchase #6	$101.75	7.720%	$109.6051	$109.61	$109.60	$109.60
Purchase #7	$45.82	8.822%	$49.8622	$49.86	$49.85	$49.90
7 purchase totals =	$745.14		$815.1738	$815.17	$815.20	$815.20