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	$80.31	3.110%	$82.8076	$82.81	$82.80	$82.80
Purchase #2	$207.96	9.203%	$227.0986	$227.10	$227.10	$227.10
Purchase #3	$49.83	7.604%	$53.6191	$53.62	$53.60	$53.60
Purchase #4	$173.53	8.765%	$188.7399	$188.74	$188.75	$188.70
Purchase #5	$120.31	8.490%	$130.5243	$130.52	$130.50	$130.50
Purchase #6	$90.87	7.369%	$97.5662	$97.57	$97.55	$97.60
Purchase #7	$187.79	5.759%	$198.6048	$198.60	$198.60	$198.60
7 purchase totals =	$910.60		$978.9605	$978.96	$978.90	$978.90