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	$41.77	7.809%	$45.0318	$45.03	$45.05	$45.00
Purchase #2	$21.50	13.110%	$24.3187	$24.32	$24.30	$24.30
Purchase #3	$165.56	9.464%	$181.2286	$181.23	$181.25	$181.20
Purchase #4	$97.87	8.536%	$106.2242	$106.22	$106.20	$106.20
Purchase #5	$147.47	7.709%	$158.8385	$158.84	$158.85	$158.80
Purchase #6	$39.44	8.720%	$42.8792	$42.88	$42.90	$42.90
Purchase #7	$37.89	9.786%	$41.5979	$41.60	$41.60	$41.60
7 purchase totals =	$551.50		$600.1189	$600.12	$600.15	$600.00