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	$38.46	13.674%	$43.719	$43.72	$43.70	$43.70
Purchase #2	$119.51	3.811%	$124.0645	$124.06	$124.05	$124.10
Purchase #3	$18.85	8.591%	$20.4694	$20.47	$20.45	$20.50
Purchase #4	$60.61	3.298%	$62.6089	$62.61	$62.60	$62.60
Purchase #5	$221.39	3.113%	$228.2819	$228.28	$228.30	$228.30
Purchase #6	$31.95	3.597%	$33.0992	$33.10	$33.10	$33.10
Purchase #7	$103.74	3.581%	$107.4549	$107.45	$107.45	$107.50
7 purchase totals =	$594.51		$619.6978	$619.69	$619.65	$619.80