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	$143.86	13.664%	$163.517	$163.52	$163.50	$163.50
Purchase #2	$153.86	7.865%	$165.9611	$165.96	$165.95	$166.00
Purchase #3	$93.28	7.565%	$100.3366	$100.34	$100.35	$100.30
Purchase #4	$33.72	10.613%	$37.2987	$37.30	$37.30	$37.30
Purchase #5	$96.27	7.399%	$103.393	$103.39	$103.40	$103.40
Purchase #6	$144.28	6.817%	$154.1156	$154.12	$154.10	$154.10
Purchase #7	$232.51	3.310%	$240.2061	$240.21	$240.20	$240.20
7 purchase totals =	$897.78		$964.8281	$964.84	$964.80	$964.80