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	$221.72	12.748%	$249.9849	$249.98	$250.00	$250.00
Purchase #2	$107.41	3.455%	$111.121	$111.12	$111.10	$111.10
Purchase #3	$53.72	10.558%	$59.3918	$59.39	$59.40	$59.40
Purchase #4	$71.71	7.398%	$77.0151	$77.02	$77.00	$77.00
Purchase #5	$108.75	12.845%	$122.7189	$122.72	$122.70	$122.70
Purchase #6	$40.98	7.524%	$44.0633	$44.06	$44.05	$44.10
Purchase #7	$67.41	7.229%	$72.2831	$72.28	$72.30	$72.30
7 purchase totals =	$671.70		$736.5781	$736.57	$736.55	$736.60