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	$85.76	5.638%	$90.5951	$90.60	$90.60	$90.60
Purchase #2	$174.49	8.164%	$188.7354	$188.74	$188.75	$188.70
Purchase #3	$11.55	6.719%	$12.326	$12.33	$12.35	$12.30
Purchase #4	$62.84	12.708%	$70.8257	$70.83	$70.85	$70.80
Purchase #5	$132.29	9.198%	$144.458	$144.46	$144.45	$144.50
Purchase #6	$59.57	8.655%	$64.7258	$64.73	$64.75	$64.70
Purchase #7	$102.79	6.334%	$109.3007	$109.30	$109.30	$109.30
7 purchase totals =	$629.29		$680.9667	$680.99	$681.05	$680.90