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	$40.71	11.485%	$45.3855	$45.39	$45.40	$45.40
Purchase #2	$124.51	10.516%	$137.6035	$137.60	$137.60	$137.60
Purchase #3	$183.44	4.392%	$191.4967	$191.50	$191.50	$191.50
Purchase #4	$13.33	12.578%	$15.0066	$15.01	$15.00	$15.00
Purchase #5	$131.70	11.823%	$147.2709	$147.27	$147.25	$147.30
Purchase #6	$47.79	11.338%	$53.2084	$53.21	$53.20	$53.20
Purchase #7	$17.52	4.459%	$18.3012	$18.30	$18.30	$18.30
7 purchase totals =	$559.00		$608.2728	$608.28	$608.25	$608.30