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	$82.72	9.644%	$90.6975	$90.70	$90.70	$90.70
Purchase #2	$147.77	5.453%	$155.8279	$155.83	$155.85	$155.80
Purchase #3	$249.38	5.491%	$263.0735	$263.07	$263.05	$263.10
Purchase #4	$18.98	12.241%	$21.3033	$21.30	$21.30	$21.30
Purchase #5	$71.36	10.189%	$78.6309	$78.63	$78.65	$78.60
Purchase #6	$98.66	12.326%	$110.8208	$110.82	$110.80	$110.80
Purchase #7	$225.87	3.590%	$233.9787	$233.98	$234.00	$234.00
7 purchase totals =	$894.74		$954.3326	$954.33	$954.35	$954.30