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	$17.55	4.190%	$18.2853	$18.29	$18.30	$18.30
Purchase #2	$185.76	10.554%	$205.3651	$205.37	$205.35	$205.40
Purchase #3	$206.96	9.745%	$227.1283	$227.13	$227.15	$227.10
Purchase #4	$215.73	8.217%	$233.4565	$233.46	$233.45	$233.50
Purchase #5	$45.47	3.242%	$46.9441	$46.94	$46.95	$46.90
Purchase #6	$62.52	4.805%	$65.5241	$65.52	$65.50	$65.50
Purchase #7	$93.31	5.599%	$98.5344	$98.53	$98.55	$98.50
7 purchase totals =	$827.30		$895.2378	$895.24	$895.25	$895.20