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	$153.78	10.708%	$170.2468	$170.25	$170.25	$170.20
Purchase #2	$99.32	12.358%	$111.594	$111.59	$111.60	$111.60
Purchase #3	$74.63	6.860%	$79.7496	$79.75	$79.75	$79.70
Purchase #4	$181.78	13.286%	$205.9313	$205.93	$205.95	$205.90
Purchase #5	$102.78	6.841%	$109.8112	$109.81	$109.80	$109.80
Purchase #6	$32.31	13.674%	$36.7281	$36.73	$36.75	$36.70
Purchase #7	$177.41	12.427%	$199.4567	$199.46	$199.45	$199.50
7 purchase totals =	$822.01		$913.5177	$913.52	$913.55	$913.40