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	$150.81	5.794%	$159.5479	$159.55	$159.55	$159.50
Purchase #2	$205.82	10.558%	$227.5505	$227.55	$227.55	$227.60
Purchase #3	$171.42	6.767%	$183.02	$183.02	$183.00	$183.00
Purchase #4	$13.45	9.828%	$14.7719	$14.77	$14.75	$14.80
Purchase #5	$99.89	11.661%	$111.5382	$111.54	$111.55	$111.50
Purchase #6	$89.62	6.383%	$95.3404	$95.34	$95.35	$95.30
Purchase #7	$71.52	12.267%	$80.2934	$80.29	$80.30	$80.30
7 purchase totals =	$802.53		$872.0623	$872.06	$872.05	$872.00