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	$237.96	7.798%	$256.5161	$256.52	$256.50	$256.50
Purchase #2	$47.36	4.582%	$49.53	$49.53	$49.55	$49.50
Purchase #3	$88.91	10.623%	$98.3549	$98.35	$98.35	$98.40
Purchase #4	$231.34	5.729%	$244.5935	$244.59	$244.60	$244.60
Purchase #5	$190.61	10.304%	$210.2505	$210.25	$210.25	$210.30
Purchase #6	$151.39	7.380%	$162.5626	$162.56	$162.55	$162.60
Purchase #7	$235.82	9.418%	$258.0295	$258.03	$258.05	$258.00
7 purchase totals =	$1,183.39		$1,279.8371	$1,279.83	$1,279.85	$1,279.90