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	$85.58	9.685%	$93.8684	$93.87	$93.85	$93.90
Purchase #2	$117.72	4.735%	$123.294	$123.29	$123.30	$123.30
Purchase #3	$111.35	9.804%	$122.2668	$122.27	$122.25	$122.30
Purchase #4	$168.58	3.153%	$173.8953	$173.90	$173.90	$173.90
Purchase #5	$82.63	9.867%	$90.7831	$90.78	$90.80	$90.80
Purchase #6	$123.72	10.658%	$136.9061	$136.91	$136.90	$136.90
Purchase #7	$85.48	7.343%	$91.7568	$91.76	$91.75	$91.80
7 purchase totals =	$775.06		$832.7705	$832.78	$832.75	$832.90