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	$75.75	11.532%	$84.4855	$84.49	$84.50	$84.50
Purchase #2	$37.80	13.313%	$42.8323	$42.83	$42.85	$42.80
Purchase #3	$79.36	13.740%	$90.2641	$90.26	$90.25	$90.30
Purchase #4	$101.56	10.260%	$111.9801	$111.98	$112.00	$112.00
Purchase #5	$45.95	9.758%	$50.4338	$50.43	$50.45	$50.40
Purchase #6	$123.85	7.275%	$132.8601	$132.86	$132.85	$132.90
Purchase #7	$204.41	7.644%	$220.0351	$220.04	$220.05	$220.00
7 purchase totals =	$668.68		$732.8910	$732.89	$732.95	$732.90