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	$120.66	5.740%	$127.5859	$127.59	$127.60	$127.60
Purchase #2	$85.25	4.734%	$89.2857	$89.29	$89.30	$89.30
Purchase #3	$14.98	11.625%	$16.7214	$16.72	$16.70	$16.70
Purchase #4	$232.28	11.359%	$258.6647	$258.66	$258.65	$258.70
Purchase #5	$246.99	9.460%	$270.3553	$270.36	$270.35	$270.40
Purchase #6	$104.52	5.136%	$109.8881	$109.89	$109.90	$109.90
Purchase #7	$34.45	8.675%	$37.4385	$37.44	$37.45	$37.40
7 purchase totals =	$839.13		$909.9396	$909.95	$909.95	$910.00