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	$19.63	13.842%	$22.3472	$22.35	$22.35	$22.30
Purchase #2	$191.40	9.137%	$208.8882	$208.89	$208.90	$208.90
Purchase #3	$28.38	3.151%	$29.2743	$29.27	$29.25	$29.30
Purchase #4	$18.63	8.553%	$20.2234	$20.22	$20.20	$20.20
Purchase #5	$120.65	6.424%	$128.4006	$128.40	$128.40	$128.40
Purchase #6	$143.67	3.293%	$148.4011	$148.40	$148.40	$148.40
Purchase #7	$81.26	11.233%	$90.3879	$90.39	$90.40	$90.40
7 purchase totals =	$603.62		$647.9227	$647.92	$647.90	$647.90