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	$166.27	8.504%	$180.4096	$180.41	$180.40	$180.40
Purchase #2	$85.80	12.184%	$96.2539	$96.25	$96.25	$96.30
Purchase #3	$86.97	4.506%	$90.8889	$90.89	$90.90	$90.90
Purchase #4	$40.27	3.747%	$41.7789	$41.78	$41.80	$41.80
Purchase #5	$170.84	10.705%	$189.1284	$189.13	$189.15	$189.10
Purchase #6	$18.45	10.149%	$20.3225	$20.32	$20.30	$20.30
Purchase #7	$191.92	8.683%	$208.5844	$208.58	$208.60	$208.60
7 purchase totals =	$760.52		$827.3666	$827.36	$827.40	$827.40