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	$145.82	13.687%	$165.7784	$165.78	$165.80	$165.80
Purchase #2	$153.61	5.499%	$162.057	$162.06	$162.05	$162.10
Purchase #3	$92.47	10.112%	$101.8206	$101.82	$101.80	$101.80
Purchase #4	$117.57	7.404%	$126.2749	$126.27	$126.25	$126.30
Purchase #5	$76.40	11.534%	$85.212	$85.21	$85.20	$85.20
Purchase #6	$90.25	13.272%	$102.228	$102.23	$102.25	$102.20
Purchase #7	$48.43	9.684%	$53.12	$53.12	$53.10	$53.10
7 purchase totals =	$724.55		$796.4909	$796.49	$796.45	$796.50