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	$134.89	7.721%	$145.3049	$145.30	$145.30	$145.30
Purchase #2	$98.67	12.744%	$111.2445	$111.24	$111.25	$111.20
Purchase #3	$73.93	11.375%	$82.3395	$82.34	$82.35	$82.30
Purchase #4	$87.31	3.795%	$90.6234	$90.62	$90.60	$90.60
Purchase #5	$235.57	11.528%	$262.7265	$262.73	$262.75	$262.70
Purchase #6	$7.89	5.691%	$8.339	$8.34	$8.35	$8.30
Purchase #7	$74.27	9.141%	$81.059	$81.06	$81.05	$81.10
7 purchase totals =	$712.53		$781.6368	$781.63	$781.65	$781.50