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	$69.88	11.812%	$78.1342	$78.13	$78.15	$78.10
Purchase #2	$156.87	7.504%	$168.6415	$168.64	$168.65	$168.60
Purchase #3	$38.79	5.399%	$40.8843	$40.88	$40.90	$40.90
Purchase #4	$123.52	3.483%	$127.8222	$127.82	$127.80	$127.80
Purchase #5	$30.74	4.523%	$32.1304	$32.13	$32.15	$32.10
Purchase #6	$220.69	9.727%	$242.1565	$242.16	$242.15	$242.20
Purchase #7	$52.37	11.739%	$58.5177	$58.52	$58.50	$58.50
7 purchase totals =	$692.86		$748.2868	$748.28	$748.30	$748.20