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	$39.67	6.675%	$42.318	$42.32	$42.30	$42.30
Purchase #2	$219.35	9.351%	$239.8614	$239.86	$239.85	$239.90
Purchase #3	$40.74	7.554%	$43.8175	$43.82	$43.80	$43.80
Purchase #4	$45.83	10.681%	$50.7251	$50.73	$50.75	$50.70
Purchase #5	$177.81	4.283%	$185.4256	$185.43	$185.45	$185.40
Purchase #6	$242.67	3.314%	$250.7121	$250.71	$250.70	$250.70
Purchase #7	$21.58	5.723%	$22.815	$22.82	$22.80	$22.80
7 purchase totals =	$787.65		$835.6747	$835.69	$835.65	$835.60