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	$29.32	12.433%	$32.9654	$32.97	$32.95	$33.00
Purchase #2	$137.77	7.552%	$148.1744	$148.17	$148.15	$148.20
Purchase #3	$38.55	9.476%	$42.203	$42.20	$42.20	$42.20
Purchase #4	$236.64	9.119%	$258.2192	$258.22	$258.20	$258.20
Purchase #5	$69.77	4.325%	$72.7876	$72.79	$72.80	$72.80
Purchase #6	$148.83	11.128%	$165.3918	$165.39	$165.40	$165.40
Purchase #7	$108.88	13.745%	$123.8456	$123.85	$123.85	$123.80
7 purchase totals =	$769.76		$843.5870	$843.59	$843.55	$843.60