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	$228.96	11.471%	$255.224	$255.22	$255.20	$255.20
Purchase #2	$189.43	5.631%	$200.0968	$200.10	$200.10	$200.10
Purchase #3	$234.30	5.470%	$247.1162	$247.12	$247.10	$247.10
Purchase #4	$95.35	5.478%	$100.5733	$100.57	$100.55	$100.60
Purchase #5	$21.79	5.197%	$22.9224	$22.92	$22.90	$22.90
Purchase #6	$34.41	8.212%	$37.2357	$37.24	$37.25	$37.20
Purchase #7	$127.63	9.143%	$139.2992	$139.30	$139.30	$139.30
7 purchase totals =	$931.87		$1,002.4676	$1,002.47	$1,002.40	$1,002.40