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	$230.90	7.776%	$248.8548	$248.85	$248.85	$248.90
Purchase #2	$71.45	9.666%	$78.3564	$78.36	$78.35	$78.40
Purchase #3	$225.60	5.865%	$238.8314	$238.83	$238.85	$238.80
Purchase #4	$129.97	11.791%	$145.2948	$145.29	$145.30	$145.30
Purchase #5	$119.69	9.366%	$130.9002	$130.90	$130.90	$130.90
Purchase #6	$43.56	4.695%	$45.6051	$45.61	$45.60	$45.60
Purchase #7	$221.61	10.852%	$245.6591	$245.66	$245.65	$245.70
7 purchase totals =	$1,042.78		$1,133.5018	$1,133.50	$1,133.50	$1,133.60