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	$16.58	5.592%	$17.5072	$17.51	$17.50	$17.50
Purchase #2	$125.60	9.279%	$137.2544	$137.25	$137.25	$137.30
Purchase #3	$59.63	10.209%	$65.7176	$65.72	$65.70	$65.70
Purchase #4	$52.32	13.811%	$59.5459	$59.55	$59.55	$59.50
Purchase #5	$106.37	11.479%	$118.5802	$118.58	$118.60	$118.60
Purchase #6	$223.35	13.498%	$253.4978	$253.50	$253.50	$253.50
Purchase #7	$193.30	13.150%	$218.719	$218.72	$218.70	$218.70
7 purchase totals =	$777.15		$870.8221	$870.83	$870.80	$870.80