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	$39.28	10.156%	$43.2693	$43.27	$43.25	$43.30
Purchase #2	$53.72	7.615%	$57.8108	$57.81	$57.80	$57.80
Purchase #3	$100.38	8.654%	$109.0669	$109.07	$109.05	$109.10
Purchase #4	$136.85	4.561%	$143.0917	$143.09	$143.10	$143.10
Purchase #5	$211.79	12.769%	$238.8335	$238.83	$238.85	$238.80
Purchase #6	$26.73	5.663%	$28.2437	$28.24	$28.25	$28.20
Purchase #7	$78.64	7.161%	$84.2714	$84.27	$84.25	$84.30
7 purchase totals =	$647.39		$704.5873	$704.58	$704.55	$704.60