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	$81.95	8.498%	$88.9141	$88.91	$88.90	$88.90
Purchase #2	$101.69	12.435%	$114.3352	$114.34	$114.35	$114.30
Purchase #3	$48.50	10.589%	$53.6357	$53.64	$53.65	$53.60
Purchase #4	$36.60	5.347%	$38.557	$38.56	$38.55	$38.60
Purchase #5	$59.39	5.209%	$62.4836	$62.48	$62.50	$62.50
Purchase #6	$163.83	9.721%	$179.7559	$179.76	$179.75	$179.80
Purchase #7	$56.81	8.196%	$61.4661	$61.47	$61.45	$61.50
7 purchase totals =	$548.77		$599.1476	$599.16	$599.15	$599.20