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	$16.50	4.298%	$17.2092	$17.21	$17.20	$17.20
Purchase #2	$134.99	5.314%	$142.1634	$142.16	$142.15	$142.20
Purchase #3	$236.81	11.472%	$263.9768	$263.98	$264.00	$264.00
Purchase #4	$28.37	11.419%	$31.6096	$31.61	$31.60	$31.60
Purchase #5	$52.90	8.396%	$57.3415	$57.34	$57.35	$57.30
Purchase #6	$139.74	7.599%	$150.3588	$150.36	$150.35	$150.40
Purchase #7	$90.85	9.615%	$99.5852	$99.59	$99.60	$99.60
7 purchase totals =	$700.16		$762.2445	$762.25	$762.25	$762.30