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	$78.61	9.828%	$86.3358	$86.34	$86.35	$86.30
Purchase #2	$150.53	10.214%	$165.9051	$165.91	$165.90	$165.90
Purchase #3	$135.78	6.630%	$144.7822	$144.78	$144.80	$144.80
Purchase #4	$112.43	10.257%	$123.9619	$123.96	$123.95	$124.00
Purchase #5	$146.95	4.221%	$153.1528	$153.15	$153.15	$153.20
Purchase #6	$130.44	10.855%	$144.5993	$144.60	$144.60	$144.60
Purchase #7	$144.28	5.824%	$152.6829	$152.68	$152.70	$152.70
7 purchase totals =	$899.02		$971.4200	$971.42	$971.45	$971.50