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	$14.27	3.587%	$14.7819	$14.78	$14.80	$14.80
Purchase #2	$240.29	10.245%	$264.9077	$264.91	$264.90	$264.90
Purchase #3	$91.86	9.841%	$100.8999	$100.90	$100.90	$100.90
Purchase #4	$127.66	10.466%	$141.0209	$141.02	$141.00	$141.00
Purchase #5	$59.48	11.468%	$66.3012	$66.30	$66.30	$66.30
Purchase #6	$106.36	8.115%	$114.9911	$114.99	$115.00	$115.00
Purchase #7	$53.35	13.487%	$60.5453	$60.55	$60.55	$60.50
7 purchase totals =	$693.27		$763.4480	$763.45	$763.45	$763.40