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	$133.61	10.690%	$147.8929	$147.89	$147.90	$147.90
Purchase #2	$235.52	8.866%	$256.4012	$256.40	$256.40	$256.40
Purchase #3	$74.27	9.552%	$81.3643	$81.36	$81.35	$81.40
Purchase #4	$36.55	3.227%	$37.7295	$37.73	$37.75	$37.70
Purchase #5	$152.39	10.778%	$168.8146	$168.81	$168.80	$168.80
Purchase #6	$40.37	4.156%	$42.0478	$42.05	$42.05	$42.00
Purchase #7	$89.43	7.144%	$95.8189	$95.82	$95.80	$95.80
7 purchase totals =	$762.14		$830.0692	$830.06	$830.05	$830.00