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	$51.67	7.370%	$55.4781	$55.48	$55.50	$55.50
Purchase #2	$227.27	5.104%	$238.8699	$238.87	$238.85	$238.90
Purchase #3	$51.80	9.154%	$56.5418	$56.54	$56.55	$56.50
Purchase #4	$165.81	3.862%	$172.2136	$172.21	$172.20	$172.20
Purchase #5	$210.96	9.202%	$230.3725	$230.37	$230.35	$230.40
Purchase #6	$196.77	12.143%	$220.6638	$220.66	$220.65	$220.70
Purchase #7	$84.57	6.851%	$90.3639	$90.36	$90.35	$90.40
7 purchase totals =	$988.85		$1,064.5036	$1,064.49	$1,064.45	$1,064.60