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	$225.35	3.796%	$233.9043	$233.90	$233.90	$233.90
Purchase #2	$186.59	12.460%	$209.8391	$209.84	$209.85	$209.80
Purchase #3	$59.66	7.495%	$64.1315	$64.13	$64.15	$64.10
Purchase #4	$217.52	5.451%	$229.377	$229.38	$229.40	$229.40
Purchase #5	$171.94	12.150%	$192.8307	$192.83	$192.85	$192.80
Purchase #6	$53.52	3.450%	$55.3664	$55.37	$55.35	$55.40
Purchase #7	$14.28	4.679%	$14.9482	$14.95	$14.95	$14.90
7 purchase totals =	$928.86		$1,000.3972	$1,000.40	$1,000.45	$1,000.30