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	$89.79	11.747%	$100.3376	$100.34	$100.35	$100.30
Purchase #2	$40.97	3.520%	$42.4121	$42.41	$42.40	$42.40
Purchase #3	$167.72	6.688%	$178.9371	$178.94	$178.95	$178.90
Purchase #4	$39.94	7.828%	$43.0665	$43.07	$43.05	$43.10
Purchase #5	$190.55	9.827%	$209.2753	$209.28	$209.30	$209.30
Purchase #6	$64.30	7.568%	$69.1662	$69.17	$69.15	$69.20
Purchase #7	$156.29	12.137%	$175.2589	$175.26	$175.25	$175.30
7 purchase totals =	$749.56		$818.4537	$818.47	$818.45	$818.50