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	$233.59	8.851%	$254.2651	$254.27	$254.25	$254.30
Purchase #2	$67.68	7.493%	$72.7513	$72.75	$72.75	$72.80
Purchase #3	$132.78	7.255%	$142.4132	$142.41	$142.40	$142.40
Purchase #4	$61.80	10.659%	$68.3873	$68.39	$68.40	$68.40
Purchase #5	$146.48	13.293%	$165.9516	$165.95	$165.95	$166.00
Purchase #6	$75.83	12.549%	$85.3459	$85.35	$85.35	$85.30
Purchase #7	$151.81	13.289%	$171.984	$171.98	$172.00	$172.00
7 purchase totals =	$869.97		$961.0984	$961.10	$961.10	$961.20