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	$21.80	10.383%	$24.0635	$24.06	$24.05	$24.10
Purchase #2	$139.30	10.178%	$153.478	$153.48	$153.50	$153.50
Purchase #3	$84.29	7.279%	$90.4255	$90.43	$90.45	$90.40
Purchase #4	$145.77	11.755%	$162.9053	$162.91	$162.90	$162.90
Purchase #5	$178.73	6.488%	$190.326	$190.33	$190.35	$190.30
Purchase #6	$99.28	4.617%	$103.8638	$103.86	$103.85	$103.90
Purchase #7	$61.27	4.722%	$64.1632	$64.16	$64.15	$64.20
7 purchase totals =	$730.44		$789.2253	$789.23	$789.25	$789.30