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	$236.67	3.708%	$245.4457	$245.45	$245.45	$245.40
Purchase #2	$94.48	5.109%	$99.307	$99.31	$99.30	$99.30
Purchase #3	$245.53	7.139%	$263.0584	$263.06	$263.05	$263.10
Purchase #4	$132.41	4.277%	$138.0732	$138.07	$138.05	$138.10
Purchase #5	$36.49	12.627%	$41.0976	$41.10	$41.10	$41.10
Purchase #6	$58.54	12.758%	$66.0085	$66.01	$66.00	$66.00
Purchase #7	$116.52	10.319%	$128.5437	$128.54	$128.55	$128.50
7 purchase totals =	$920.64		$981.5341	$981.54	$981.50	$981.50