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	$145.72	7.274%	$156.3197	$156.32	$156.30	$156.30
Purchase #2	$167.27	13.380%	$189.6507	$189.65	$189.65	$189.70
Purchase #3	$36.76	3.176%	$37.9275	$37.93	$37.95	$37.90
Purchase #4	$40.35	8.829%	$43.9125	$43.91	$43.90	$43.90
Purchase #5	$142.98	8.841%	$155.6209	$155.62	$155.60	$155.60
Purchase #6	$105.88	5.374%	$111.57	$111.57	$111.55	$111.60
Purchase #7	$111.57	5.531%	$117.7409	$117.74	$117.75	$117.70
7 purchase totals =	$750.53		$812.7422	$812.74	$812.70	$812.70