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	$27.94	5.141%	$29.3764	$29.38	$29.40	$29.40
Purchase #2	$92.37	4.181%	$96.232	$96.23	$96.25	$96.20
Purchase #3	$140.72	7.227%	$150.8898	$150.89	$150.90	$150.90
Purchase #4	$82.30	3.349%	$85.0562	$85.06	$85.05	$85.10
Purchase #5	$100.52	5.142%	$105.6887	$105.69	$105.70	$105.70
Purchase #6	$248.35	5.279%	$261.4604	$261.46	$261.45	$261.50
Purchase #7	$219.68	6.791%	$234.5985	$234.60	$234.60	$234.60
7 purchase totals =	$911.88		$963.3020	$963.31	$963.35	$963.40