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	$220.51	3.602%	$228.4528	$228.45	$228.45	$228.50
Purchase #2	$31.33	7.800%	$33.7737	$33.77	$33.75	$33.80
Purchase #3	$38.55	12.376%	$43.3209	$43.32	$43.30	$43.30
Purchase #4	$114.35	3.367%	$118.2002	$118.20	$118.20	$118.20
Purchase #5	$126.56	10.252%	$139.5349	$139.53	$139.55	$139.50
Purchase #6	$156.64	13.501%	$177.788	$177.79	$177.80	$177.80
Purchase #7	$55.66	7.338%	$59.7443	$59.74	$59.75	$59.70
7 purchase totals =	$743.60		$800.8148	$800.80	$800.80	$800.80