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	$173.70	6.664%	$185.2754	$185.28	$185.30	$185.30
Purchase #2	$176.87	9.411%	$193.5152	$193.52	$193.50	$193.50
Purchase #3	$112.29	7.335%	$120.5265	$120.53	$120.55	$120.50
Purchase #4	$221.91	11.213%	$246.7928	$246.79	$246.80	$246.80
Purchase #5	$37.45	5.588%	$39.5427	$39.54	$39.55	$39.50
Purchase #6	$53.47	12.150%	$59.9666	$59.97	$59.95	$60.00
Purchase #7	$243.48	8.400%	$263.9323	$263.93	$263.95	$263.90
7 purchase totals =	$1,019.17		$1,109.5515	$1,109.56	$1,109.60	$1,109.50