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	$239.66	6.597%	$255.4704	$255.47	$255.45	$255.50
Purchase #2	$93.35	11.616%	$104.1935	$104.19	$104.20	$104.20
Purchase #3	$231.54	3.778%	$240.2876	$240.29	$240.30	$240.30
Purchase #4	$127.36	13.181%	$144.1473	$144.15	$144.15	$144.10
Purchase #5	$238.49	8.512%	$258.7903	$258.79	$258.80	$258.80
Purchase #6	$5.89	8.208%	$6.3735	$6.37	$6.35	$6.40
Purchase #7	$152.94	11.729%	$170.8783	$170.88	$170.90	$170.90
7 purchase totals =	$1,089.23		$1,180.1409	$1,180.14	$1,180.15	$1,180.20