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	$38.67	9.767%	$42.4469	$42.45	$42.45	$42.40
Purchase #2	$221.42	7.696%	$238.4605	$238.46	$238.45	$238.50
Purchase #3	$191.62	9.383%	$209.5997	$209.60	$209.60	$209.60
Purchase #4	$124.73	9.512%	$136.5943	$136.59	$136.60	$136.60
Purchase #5	$58.26	13.727%	$66.2574	$66.26	$66.25	$66.30
Purchase #6	$144.83	13.444%	$164.3009	$164.30	$164.30	$164.30
Purchase #7	$86.76	4.108%	$90.3241	$90.32	$90.30	$90.30
7 purchase totals =	$866.29		$947.9838	$947.98	$947.95	$948.00