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	$112.74	6.739%	$120.3375	$120.34	$120.35	$120.30
Purchase #2	$31.55	3.336%	$32.6025	$32.60	$32.60	$32.60
Purchase #3	$77.79	9.559%	$85.2259	$85.23	$85.25	$85.20
Purchase #4	$128.48	10.543%	$142.0256	$142.03	$142.05	$142.00
Purchase #5	$136.75	5.111%	$143.7393	$143.74	$143.75	$143.70
Purchase #6	$117.94	4.810%	$123.6129	$123.61	$123.60	$123.60
Purchase #7	$49.52	6.684%	$52.8299	$52.83	$52.85	$52.80
7 purchase totals =	$654.77		$700.3736	$700.38	$700.45	$700.20