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	$129.67	7.793%	$139.7752	$139.78	$139.80	$139.80
Purchase #2	$112.40	4.506%	$117.4647	$117.46	$117.45	$117.50
Purchase #3	$109.47	13.153%	$123.8686	$123.87	$123.85	$123.90
Purchase #4	$132.36	12.518%	$148.9288	$148.93	$148.95	$148.90
Purchase #5	$130.75	13.442%	$148.3254	$148.33	$148.35	$148.30
Purchase #6	$19.85	6.718%	$21.1835	$21.18	$21.20	$21.20
Purchase #7	$30.59	9.852%	$33.6037	$33.60	$33.60	$33.60
7 purchase totals =	$665.09		$733.1499	$733.15	$733.20	$733.20