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	$206.27	13.673%	$234.4733	$234.47	$234.45	$234.50
Purchase #2	$226.53	6.171%	$240.5092	$240.51	$240.50	$240.50
Purchase #3	$120.46	6.395%	$128.1634	$128.16	$128.15	$128.20
Purchase #4	$65.40	10.705%	$72.4011	$72.40	$72.40	$72.40
Purchase #5	$124.56	7.630%	$134.0639	$134.06	$134.05	$134.10
Purchase #6	$224.80	10.430%	$248.2466	$248.25	$248.25	$248.20
Purchase #7	$25.90	7.355%	$27.8049	$27.80	$27.80	$27.80
7 purchase totals =	$993.92		$1,085.6624	$1,085.65	$1,085.60	$1,085.70