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	$176.65	13.421%	$200.3582	$200.36	$200.35	$200.40
Purchase #2	$53.47	11.674%	$59.7121	$59.71	$59.70	$59.70
Purchase #3	$229.68	6.737%	$245.1535	$245.15	$245.15	$245.20
Purchase #4	$216.29	9.179%	$236.1433	$236.14	$236.15	$236.10
Purchase #5	$115.42	10.344%	$127.359	$127.36	$127.35	$127.40
Purchase #6	$244.57	4.609%	$255.8422	$255.84	$255.85	$255.80
Purchase #7	$219.37	7.237%	$235.2458	$235.25	$235.25	$235.20
7 purchase totals =	$1,255.45		$1,359.8141	$1,359.81	$1,359.80	$1,359.80