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	$26.84	6.190%	$28.5014	$28.50	$28.50	$28.50
Purchase #2	$230.35	10.345%	$254.1797	$254.18	$254.20	$254.20
Purchase #3	$53.25	12.404%	$59.8551	$59.86	$59.85	$59.90
Purchase #4	$194.36	8.803%	$211.4695	$211.47	$211.45	$211.50
Purchase #5	$169.93	6.372%	$180.7579	$180.76	$180.75	$180.80
Purchase #6	$55.78	6.268%	$59.2763	$59.28	$59.30	$59.30
Purchase #7	$232.45	9.750%	$255.1139	$255.11	$255.10	$255.10
7 purchase totals =	$962.96		$1,049.1538	$1,049.16	$1,049.15	$1,049.30