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	$25.49	7.781%	$27.4734	$27.47	$27.45	$27.50
Purchase #2	$132.89	7.817%	$143.278	$143.28	$143.30	$143.30
Purchase #3	$76.78	6.419%	$81.7085	$81.71	$81.70	$81.70
Purchase #4	$131.26	8.196%	$142.0181	$142.02	$142.00	$142.00
Purchase #5	$48.63	9.527%	$53.263	$53.26	$53.25	$53.30
Purchase #6	$39.86	9.218%	$43.5343	$43.53	$43.55	$43.50
Purchase #7	$166.81	13.467%	$189.2743	$189.27	$189.25	$189.30
7 purchase totals =	$621.72		$680.5496	$680.54	$680.50	$680.60