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	$212.89	12.867%	$240.2826	$240.28	$240.30	$240.30
Purchase #2	$119.51	6.816%	$127.6558	$127.66	$127.65	$127.70
Purchase #3	$74.39	10.331%	$82.0752	$82.08	$82.10	$82.10
Purchase #4	$64.47	4.760%	$67.5388	$67.54	$67.55	$67.50
Purchase #5	$91.35	5.470%	$96.3468	$96.35	$96.35	$96.30
Purchase #6	$153.98	13.423%	$174.6487	$174.65	$174.65	$174.60
Purchase #7	$89.66	12.205%	$100.603	$100.60	$100.60	$100.60
7 purchase totals =	$806.25		$889.1509	$889.16	$889.20	$889.10