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	$12.47	11.262%	$13.8744	$13.87	$13.85	$13.90
Purchase #2	$51.86	6.837%	$55.4057	$55.41	$55.40	$55.40
Purchase #3	$203.44	3.384%	$210.3244	$210.32	$210.30	$210.30
Purchase #4	$125.47	13.561%	$142.485	$142.49	$142.50	$142.50
Purchase #5	$112.75	9.707%	$123.6946	$123.69	$123.70	$123.70
Purchase #6	$96.27	9.422%	$105.3406	$105.34	$105.35	$105.30
Purchase #7	$98.25	8.518%	$106.6189	$106.62	$106.60	$106.60
7 purchase totals =	$700.51		$757.7436	$757.74	$757.70	$757.70