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	$9.72	4.527%	$10.16	$10.16	$10.15	$10.20
Purchase #2	$135.68	12.867%	$153.1379	$153.14	$153.15	$153.10
Purchase #3	$84.82	5.375%	$89.3791	$89.38	$89.40	$89.40
Purchase #4	$63.26	11.377%	$70.4571	$70.46	$70.45	$70.50
Purchase #5	$108.63	5.661%	$114.7795	$114.78	$114.80	$114.80
Purchase #6	$240.98	5.236%	$253.5977	$253.60	$253.60	$253.60
Purchase #7	$96.37	11.500%	$107.4526	$107.45	$107.45	$107.50
7 purchase totals =	$739.46		$798.9639	$798.97	$799.00	$799.10