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	$30.87	9.820%	$33.9014	$33.90	$33.90	$33.90
Purchase #2	$5.75	7.156%	$6.1615	$6.16	$6.15	$6.20
Purchase #3	$18.65	13.455%	$21.1594	$21.16	$21.15	$21.20
Purchase #4	$127.88	8.330%	$138.5324	$138.53	$138.55	$138.50
Purchase #5	$112.69	9.477%	$123.3696	$123.37	$123.35	$123.40
Purchase #6	$84.89	11.600%	$94.7372	$94.74	$94.75	$94.70
Purchase #7	$54.28	13.114%	$61.3983	$61.40	$61.40	$61.40
7 purchase totals =	$435.01		$479.2598	$479.26	$479.25	$479.30