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	$17.47	3.247%	$18.0373	$18.04	$18.05	$18.00
Purchase #2	$169.94	7.205%	$182.1842	$182.18	$182.20	$182.20
Purchase #3	$125.42	11.578%	$139.9411	$139.94	$139.95	$139.90
Purchase #4	$95.25	4.280%	$99.3267	$99.33	$99.35	$99.30
Purchase #5	$125.75	3.449%	$130.0871	$130.09	$130.10	$130.10
Purchase #6	$39.62	4.191%	$41.2805	$41.28	$41.30	$41.30
Purchase #7	$169.45	11.192%	$188.4148	$188.41	$188.40	$188.40
7 purchase totals =	$742.90		$799.2717	$799.27	$799.35	$799.20