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	$137.55	7.238%	$147.5059	$147.51	$147.50	$147.50
Purchase #2	$19.94	6.411%	$21.2184	$21.22	$21.20	$21.20
Purchase #3	$134.85	13.151%	$152.5841	$152.58	$152.60	$152.60
Purchase #4	$196.52	3.391%	$203.184	$203.18	$203.20	$203.20
Purchase #5	$82.28	4.474%	$85.9612	$85.96	$85.95	$86.00
Purchase #6	$22.73	9.674%	$24.9289	$24.93	$24.95	$24.90
Purchase #7	$123.56	13.122%	$139.7735	$139.77	$139.75	$139.80
7 purchase totals =	$717.43		$775.1560	$775.15	$775.15	$775.20