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	$79.70	11.394%	$88.781	$88.78	$88.80	$88.80
Purchase #2	$38.62	3.240%	$39.8713	$39.87	$39.85	$39.90
Purchase #3	$80.31	11.630%	$89.6501	$89.65	$89.65	$89.70
Purchase #4	$132.86	13.258%	$150.4746	$150.47	$150.45	$150.50
Purchase #5	$63.47	3.451%	$65.6603	$65.66	$65.65	$65.70
Purchase #6	$212.91	13.118%	$240.8395	$240.84	$240.85	$240.80
Purchase #7	$72.58	8.254%	$78.5708	$78.57	$78.55	$78.60
7 purchase totals =	$680.45		$753.8476	$753.84	$753.80	$754.00