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	$228.60	7.700%	$246.2022	$246.20	$246.20	$246.20
Purchase #2	$241.40	10.457%	$266.6432	$266.64	$266.65	$266.60
Purchase #3	$134.44	6.458%	$143.1221	$143.12	$143.10	$143.10
Purchase #4	$55.47	7.446%	$59.6003	$59.60	$59.60	$59.60
Purchase #5	$64.55	9.574%	$70.73	$70.73	$70.75	$70.70
Purchase #6	$150.78	10.326%	$166.3495	$166.35	$166.35	$166.30
Purchase #7	$118.56	8.145%	$128.2167	$128.22	$128.20	$128.20
7 purchase totals =	$993.80		$1,080.8640	$1,080.86	$1,080.85	$1,080.70