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	$6.44	11.517%	$7.1817	$7.18	$7.20	$7.20
Purchase #2	$244.67	12.861%	$276.137	$276.14	$276.15	$276.10
Purchase #3	$60.89	7.642%	$65.5432	$65.54	$65.55	$65.50
Purchase #4	$240.86	7.482%	$258.8811	$258.88	$258.90	$258.90
Purchase #5	$32.94	12.361%	$37.0117	$37.01	$37.00	$37.00
Purchase #6	$167.29	7.614%	$180.0275	$180.03	$180.05	$180.00
Purchase #7	$19.30	11.835%	$21.5842	$21.58	$21.60	$21.60
7 purchase totals =	$772.39		$846.3664	$846.36	$846.45	$846.30