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	$54.62	12.273%	$61.3235	$61.32	$61.30	$61.30
Purchase #2	$180.91	8.668%	$196.5913	$196.59	$196.60	$196.60
Purchase #3	$191.30	9.159%	$208.8212	$208.82	$208.80	$208.80
Purchase #4	$168.71	7.543%	$181.4358	$181.44	$181.45	$181.40
Purchase #5	$248.78	9.791%	$273.138	$273.14	$273.15	$273.10
Purchase #6	$157.93	5.456%	$166.5467	$166.55	$166.55	$166.50
Purchase #7	$210.63	3.824%	$218.6845	$218.68	$218.70	$218.70
7 purchase totals =	$1,212.88		$1,306.5410	$1,306.54	$1,306.55	$1,306.40