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	$38.29	5.178%	$40.2727	$40.27	$40.25	$40.30
Purchase #2	$205.61	13.569%	$233.5092	$233.51	$233.50	$233.50
Purchase #3	$94.57	13.671%	$107.4987	$107.50	$107.50	$107.50
Purchase #4	$36.79	11.244%	$40.9267	$40.93	$40.95	$40.90
Purchase #5	$64.74	10.399%	$71.4723	$71.47	$71.45	$71.50
Purchase #6	$57.40	7.670%	$61.8026	$61.80	$61.80	$61.80
Purchase #7	$82.48	5.414%	$86.9455	$86.95	$86.95	$86.90
7 purchase totals =	$579.88		$642.4277	$642.43	$642.40	$642.40