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	$66.67	5.475%	$70.3202	$70.32	$70.30	$70.30
Purchase #2	$176.45	8.522%	$191.4871	$191.49	$191.50	$191.50
Purchase #3	$157.51	3.219%	$162.5802	$162.58	$162.60	$162.60
Purchase #4	$205.64	10.611%	$227.4605	$227.46	$227.45	$227.50
Purchase #5	$85.33	13.221%	$96.6115	$96.61	$96.60	$96.60
Purchase #6	$100.88	9.584%	$110.5483	$110.55	$110.55	$110.50
Purchase #7	$122.28	12.293%	$137.3119	$137.31	$137.30	$137.30
7 purchase totals =	$914.76		$996.3197	$996.32	$996.30	$996.30