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	$45.50	3.422%	$47.057	$47.06	$47.05	$47.10
Purchase #2	$58.29	11.784%	$65.1589	$65.16	$65.15	$65.20
Purchase #3	$106.82	12.298%	$119.9567	$119.96	$119.95	$120.00
Purchase #4	$55.46	9.815%	$60.9034	$60.90	$60.90	$60.90
Purchase #5	$11.95	7.597%	$12.8578	$12.86	$12.85	$12.90
Purchase #6	$96.33	9.285%	$105.2742	$105.27	$105.25	$105.30
Purchase #7	$225.60	12.770%	$254.4091	$254.41	$254.40	$254.40
7 purchase totals =	$599.95		$665.6171	$665.62	$665.55	$665.80