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	$28.51	5.224%	$29.9994	$30.00	$30.00	$30.00
Purchase #2	$211.72	10.393%	$233.7241	$233.72	$233.70	$233.70
Purchase #3	$135.45	12.552%	$152.4517	$152.45	$152.45	$152.50
Purchase #4	$248.64	6.430%	$264.6276	$264.63	$264.65	$264.60
Purchase #5	$105.32	5.787%	$111.4149	$111.41	$111.40	$111.40
Purchase #6	$205.70	3.621%	$213.1484	$213.15	$213.15	$213.10
Purchase #7	$49.40	9.539%	$54.1123	$54.11	$54.10	$54.10
7 purchase totals =	$984.74		$1,059.4784	$1,059.47	$1,059.45	$1,059.40