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	$103.45	4.677%	$108.2884	$108.29	$108.30	$108.30
Purchase #2	$121.64	9.689%	$133.4257	$133.43	$133.45	$133.40
Purchase #3	$22.98	11.748%	$25.6797	$25.68	$25.70	$25.70
Purchase #4	$174.42	12.631%	$196.451	$196.45	$196.45	$196.50
Purchase #5	$131.75	7.503%	$141.6352	$141.64	$141.65	$141.60
Purchase #6	$98.33	5.541%	$103.7785	$103.78	$103.80	$103.80
Purchase #7	$184.26	5.711%	$194.7831	$194.78	$194.80	$194.80
7 purchase totals =	$836.83		$904.0416	$904.05	$904.15	$904.10