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	$245.84	11.776%	$274.7901	$274.79	$274.80	$274.80
Purchase #2	$42.85	11.133%	$47.6205	$47.62	$47.60	$47.60
Purchase #3	$118.95	13.223%	$134.6788	$134.68	$134.70	$134.70
Purchase #4	$86.92	3.826%	$90.2456	$90.25	$90.25	$90.20
Purchase #5	$48.81	11.712%	$54.5266	$54.53	$54.55	$54.50
Purchase #6	$53.51	10.578%	$59.1703	$59.17	$59.15	$59.20
Purchase #7	$163.51	9.498%	$179.0402	$179.04	$179.05	$179.00
7 purchase totals =	$760.39		$840.0721	$840.08	$840.10	$840.00