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	$153.32	11.187%	$170.4719	$170.47	$170.45	$170.50
Purchase #2	$132.30	5.736%	$139.8887	$139.89	$139.90	$139.90
Purchase #3	$109.81	12.171%	$123.175	$123.18	$123.20	$123.20
Purchase #4	$104.90	4.440%	$109.5576	$109.56	$109.55	$109.60
Purchase #5	$114.88	9.356%	$125.6282	$125.63	$125.65	$125.60
Purchase #6	$207.39	7.454%	$222.8489	$222.85	$222.85	$222.80
Purchase #7	$33.92	13.580%	$38.5263	$38.53	$38.55	$38.50
7 purchase totals =	$856.52		$930.0966	$930.11	$930.15	$930.10