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	$32.69	11.641%	$36.4954	$36.50	$36.50	$36.50
Purchase #2	$85.93	12.294%	$96.4942	$96.49	$96.50	$96.50
Purchase #3	$137.82	7.492%	$148.1455	$148.15	$148.15	$148.10
Purchase #4	$131.37	6.229%	$139.553	$139.55	$139.55	$139.60
Purchase #5	$58.93	4.114%	$61.3544	$61.35	$61.35	$61.40
Purchase #6	$54.35	5.814%	$57.5099	$57.51	$57.50	$57.50
Purchase #7	$113.83	6.195%	$120.8818	$120.88	$120.90	$120.90
7 purchase totals =	$614.92		$660.4342	$660.43	$660.45	$660.50