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	$5.83	4.266%	$6.0787	$6.08	$6.10	$6.10
Purchase #2	$48.76	10.320%	$53.792	$53.79	$53.80	$53.80
Purchase #3	$59.69	10.583%	$66.007	$66.01	$66.00	$66.00
Purchase #4	$121.54	6.156%	$129.022	$129.02	$129.00	$129.00
Purchase #5	$87.52	13.744%	$99.5487	$99.55	$99.55	$99.50
Purchase #6	$183.34	6.137%	$194.5916	$194.59	$194.60	$194.60
Purchase #7	$170.29	12.390%	$191.3889	$191.39	$191.40	$191.40
7 purchase totals =	$676.97		$740.4289	$740.43	$740.45	$740.40