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	$38.85	12.484%	$43.7	$43.70	$43.70	$43.70
Purchase #2	$128.88	13.174%	$145.8587	$145.86	$145.85	$145.90
Purchase #3	$18.69	5.348%	$19.6895	$19.69	$19.70	$19.70
Purchase #4	$11.59	11.810%	$12.9588	$12.96	$12.95	$13.00
Purchase #5	$13.76	7.443%	$14.7842	$14.78	$14.80	$14.80
Purchase #6	$11.48	7.154%	$12.3013	$12.30	$12.30	$12.30
Purchase #7	$49.47	5.664%	$52.272	$52.27	$52.25	$52.30
7 purchase totals =	$272.72		$301.5645	$301.56	$301.55	$301.70