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	$25.29	5.871%	$26.7748	$26.77	$26.75	$26.80
Purchase #2	$156.45	3.261%	$161.5518	$161.55	$161.55	$161.60
Purchase #3	$152.74	10.766%	$169.184	$169.18	$169.20	$169.20
Purchase #4	$56.72	5.701%	$59.9536	$59.95	$59.95	$60.00
Purchase #5	$92.67	11.487%	$103.315	$103.32	$103.30	$103.30
Purchase #6	$27.77	4.573%	$29.0399	$29.04	$29.05	$29.00
Purchase #7	$82.98	7.778%	$89.4342	$89.43	$89.45	$89.40
7 purchase totals =	$594.62		$639.2533	$639.24	$639.25	$639.30