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	$212.54	3.569%	$220.1256	$220.13	$220.15	$220.10
Purchase #2	$137.51	3.488%	$142.3063	$142.31	$142.30	$142.30
Purchase #3	$225.99	12.208%	$253.5789	$253.58	$253.60	$253.60
Purchase #4	$90.47	13.784%	$102.9404	$102.94	$102.95	$102.90
Purchase #5	$96.73	7.751%	$104.2275	$104.23	$104.25	$104.20
Purchase #6	$233.30	7.218%	$250.1396	$250.14	$250.15	$250.10
Purchase #7	$22.27	5.642%	$23.5265	$23.53	$23.55	$23.50
7 purchase totals =	$1,018.81		$1,096.8448	$1,096.86	$1,096.95	$1,096.70