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	$215.26	9.556%	$235.8302	$235.83	$235.85	$235.80
Purchase #2	$107.38	4.407%	$112.1122	$112.11	$112.10	$112.10
Purchase #3	$45.73	9.498%	$50.0734	$50.07	$50.05	$50.10
Purchase #4	$41.58	5.671%	$43.938	$43.94	$43.95	$43.90
Purchase #5	$19.96	6.727%	$21.3027	$21.30	$21.30	$21.30
Purchase #6	$103.80	7.144%	$111.2155	$111.22	$111.20	$111.20
Purchase #7	$27.74	5.816%	$29.3534	$29.35	$29.35	$29.40
7 purchase totals =	$561.45		$603.8254	$603.82	$603.80	$603.80