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	$142.51	6.776%	$152.1665	$152.17	$152.15	$152.20
Purchase #2	$87.74	13.232%	$99.3498	$99.35	$99.35	$99.30
Purchase #3	$91.25	11.154%	$101.428	$101.43	$101.45	$101.40
Purchase #4	$212.45	13.677%	$241.5068	$241.51	$241.50	$241.50
Purchase #5	$172.71	12.241%	$193.8514	$193.85	$193.85	$193.90
Purchase #6	$181.80	4.310%	$189.6356	$189.64	$189.65	$189.60
Purchase #7	$113.81	6.670%	$121.4011	$121.40	$121.40	$121.40
7 purchase totals =	$1,002.27		$1,099.3392	$1,099.35	$1,099.35	$1,099.30