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	$161.93	3.374%	$167.3935	$167.39	$167.40	$167.40
Purchase #2	$141.68	5.267%	$149.1423	$149.14	$149.15	$149.10
Purchase #3	$52.95	12.786%	$59.7202	$59.72	$59.70	$59.70
Purchase #4	$64.38	8.593%	$69.9122	$69.91	$69.90	$69.90
Purchase #5	$124.26	6.666%	$132.5432	$132.54	$132.55	$132.50
Purchase #6	$82.86	8.730%	$90.0937	$90.09	$90.10	$90.10
Purchase #7	$105.90	5.350%	$111.5657	$111.57	$111.55	$111.60
7 purchase totals =	$733.96		$780.3708	$780.36	$780.35	$780.30