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	$138.83	13.821%	$158.0177	$158.02	$158.00	$158.00
Purchase #2	$53.69	9.711%	$58.9038	$58.90	$58.90	$58.90
Purchase #3	$117.31	5.578%	$123.8536	$123.85	$123.85	$123.90
Purchase #4	$221.86	8.362%	$240.4119	$240.41	$240.40	$240.40
Purchase #5	$236.26	13.232%	$267.5219	$267.52	$267.50	$267.50
Purchase #6	$249.58	8.146%	$269.9108	$269.91	$269.90	$269.90
Purchase #7	$215.86	13.103%	$244.1441	$244.14	$244.15	$244.10
7 purchase totals =	$1,233.39		$1,362.7638	$1,362.75	$1,362.70	$1,362.70