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	$172.66	6.128%	$183.2406	$183.24	$183.25	$183.20
Purchase #2	$89.56	12.269%	$100.5481	$100.55	$100.55	$100.50
Purchase #3	$119.43	12.396%	$134.2345	$134.23	$134.25	$134.20
Purchase #4	$53.68	7.264%	$57.5793	$57.58	$57.60	$57.60
Purchase #5	$116.90	8.522%	$126.8622	$126.86	$126.85	$126.90
Purchase #6	$174.31	3.522%	$180.4492	$180.45	$180.45	$180.40
Purchase #7	$244.26	12.133%	$273.8961	$273.90	$273.90	$273.90
7 purchase totals =	$970.80		$1,056.8100	$1,056.81	$1,056.85	$1,056.70