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	$105.64	3.698%	$109.5466	$109.55	$109.55	$109.50
Purchase #2	$94.88	13.692%	$107.871	$107.87	$107.85	$107.90
Purchase #3	$80.52	11.174%	$89.5173	$89.52	$89.50	$89.50
Purchase #4	$62.43	4.839%	$65.451	$65.45	$65.45	$65.50
Purchase #5	$249.34	12.322%	$280.0637	$280.06	$280.05	$280.10
Purchase #6	$23.41	7.361%	$25.1332	$25.13	$25.15	$25.10
Purchase #7	$219.51	10.673%	$242.9383	$242.94	$242.95	$242.90
7 purchase totals =	$835.73		$920.5211	$920.52	$920.50	$920.50