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	$228.98	8.526%	$248.5028	$248.50	$248.50	$248.50
Purchase #2	$181.32	3.862%	$188.3226	$188.32	$188.30	$188.30
Purchase #3	$244.81	12.510%	$275.4357	$275.44	$275.45	$275.40
Purchase #4	$141.33	6.268%	$150.1886	$150.19	$150.20	$150.20
Purchase #5	$233.28	4.464%	$243.6936	$243.69	$243.70	$243.70
Purchase #6	$238.60	11.198%	$265.3184	$265.32	$265.30	$265.30
Purchase #7	$45.54	5.858%	$48.2077	$48.21	$48.20	$48.20
7 purchase totals =	$1,313.86		$1,419.6694	$1,419.67	$1,419.65	$1,419.60