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	$131.81	6.163%	$139.9335	$139.93	$139.95	$139.90
Purchase #2	$171.87	7.540%	$184.829	$184.83	$184.85	$184.80
Purchase #3	$108.52	11.218%	$120.6938	$120.69	$120.70	$120.70
Purchase #4	$43.45	8.449%	$47.1211	$47.12	$47.10	$47.10
Purchase #5	$137.59	9.675%	$150.9018	$150.90	$150.90	$150.90
Purchase #6	$220.52	9.780%	$242.0869	$242.09	$242.10	$242.10
Purchase #7	$83.46	10.843%	$92.5096	$92.51	$92.50	$92.50
7 purchase totals =	$897.22		$978.0757	$978.07	$978.10	$978.00