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	$134.74	13.470%	$152.8895	$152.89	$152.90	$152.90
Purchase #2	$197.80	8.449%	$214.5121	$214.51	$214.50	$214.50
Purchase #3	$222.96	4.847%	$233.7669	$233.77	$233.75	$233.80
Purchase #4	$40.25	4.149%	$41.92	$41.92	$41.90	$41.90
Purchase #5	$93.62	12.372%	$105.2027	$105.20	$105.20	$105.20
Purchase #6	$11.83	9.593%	$12.9649	$12.96	$12.95	$13.00
Purchase #7	$151.91	11.173%	$168.8829	$168.88	$168.90	$168.90
7 purchase totals =	$853.11		$930.1390	$930.13	$930.10	$930.20