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	$33.46	8.412%	$36.2747	$36.27	$36.25	$36.30
Purchase #2	$220.39	13.771%	$250.7399	$250.74	$250.75	$250.70
Purchase #3	$161.81	11.156%	$179.8615	$179.86	$179.85	$179.90
Purchase #4	$119.91	3.837%	$124.5109	$124.51	$124.50	$124.50
Purchase #5	$101.58	6.684%	$108.3696	$108.37	$108.35	$108.40
Purchase #6	$229.32	11.277%	$255.1804	$255.18	$255.20	$255.20
Purchase #7	$55.43	3.176%	$57.1905	$57.19	$57.20	$57.20
7 purchase totals =	$921.90		$1,012.1275	$1,012.12	$1,012.10	$1,012.20