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	$16.88	10.801%	$18.7032	$18.70	$18.70	$18.70
Purchase #2	$29.46	12.113%	$33.0285	$33.03	$33.05	$33.00
Purchase #3	$193.96	8.239%	$209.9404	$209.94	$209.95	$209.90
Purchase #4	$72.64	13.277%	$82.2844	$82.28	$82.30	$82.30
Purchase #5	$121.57	4.874%	$127.4953	$127.50	$127.50	$127.50
Purchase #6	$83.68	13.587%	$95.0496	$95.05	$95.05	$95.00
Purchase #7	$79.56	3.308%	$82.1918	$82.19	$82.20	$82.20
7 purchase totals =	$597.75		$648.6932	$648.69	$648.75	$648.60