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	$205.87	12.484%	$231.5708	$231.57	$231.55	$231.60
Purchase #2	$160.34	3.640%	$166.1764	$166.18	$166.20	$166.20
Purchase #3	$69.39	13.564%	$78.8021	$78.80	$78.80	$78.80
Purchase #4	$43.79	3.399%	$45.2784	$45.28	$45.30	$45.30
Purchase #5	$106.59	10.277%	$117.5443	$117.54	$117.55	$117.50
Purchase #6	$233.54	13.572%	$265.236	$265.24	$265.25	$265.20
Purchase #7	$128.49	13.588%	$145.9492	$145.95	$145.95	$145.90
7 purchase totals =	$948.01		$1,050.5572	$1,050.56	$1,050.60	$1,050.50