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	$28.71	4.791%	$30.0855	$30.09	$30.10	$30.10
Purchase #2	$76.41	7.691%	$82.2867	$82.29	$82.30	$82.30
Purchase #3	$185.64	12.516%	$208.8747	$208.87	$208.85	$208.90
Purchase #4	$106.71	4.501%	$111.513	$111.51	$111.50	$111.50
Purchase #5	$139.81	12.202%	$156.8696	$156.87	$156.85	$156.90
Purchase #6	$81.73	10.609%	$90.4007	$90.40	$90.40	$90.40
Purchase #7	$186.52	4.371%	$194.6728	$194.67	$194.65	$194.70
7 purchase totals =	$805.53		$874.7030	$874.70	$874.65	$874.80