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	$97.84	12.197%	$109.7735	$109.77	$109.75	$109.80
Purchase #2	$240.71	12.135%	$269.9202	$269.92	$269.90	$269.90
Purchase #3	$48.86	3.151%	$50.3996	$50.40	$50.40	$50.40
Purchase #4	$124.64	13.497%	$141.4627	$141.46	$141.45	$141.50
Purchase #5	$99.80	5.439%	$105.2281	$105.23	$105.25	$105.20
Purchase #6	$150.99	6.381%	$160.6247	$160.62	$160.60	$160.60
Purchase #7	$243.49	3.521%	$252.0633	$252.06	$252.05	$252.10
7 purchase totals =	$1,006.33		$1,089.4721	$1,089.46	$1,089.40	$1,089.50