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	$245.49	11.582%	$273.9227	$273.92	$273.90	$273.90
Purchase #2	$158.94	6.246%	$168.8674	$168.87	$168.85	$168.90
Purchase #3	$116.37	13.582%	$132.1754	$132.18	$132.20	$132.20
Purchase #4	$249.71	9.391%	$273.1603	$273.16	$273.15	$273.20
Purchase #5	$177.35	8.171%	$191.8413	$191.84	$191.85	$191.80
Purchase #6	$244.52	4.609%	$255.7899	$255.79	$255.80	$255.80
Purchase #7	$60.73	11.455%	$67.6866	$67.69	$67.70	$67.70
7 purchase totals =	$1,253.11		$1,363.4436	$1,363.45	$1,363.45	$1,363.50