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	$243.28	6.279%	$258.5556	$258.56	$258.55	$258.60
Purchase #2	$112.26	11.452%	$125.116	$125.12	$125.10	$125.10
Purchase #3	$19.59	10.552%	$21.6571	$21.66	$21.65	$21.70
Purchase #4	$182.93	4.637%	$191.4125	$191.41	$191.40	$191.40
Purchase #5	$73.82	4.138%	$76.8747	$76.87	$76.85	$76.90
Purchase #6	$82.32	8.352%	$89.1954	$89.20	$89.20	$89.20
Purchase #7	$144.36	6.393%	$153.5889	$153.59	$153.60	$153.60
7 purchase totals =	$858.56		$916.4002	$916.41	$916.35	$916.50