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	$101.89	10.381%	$112.4672	$112.47	$112.45	$112.50
Purchase #2	$109.55	12.858%	$123.6359	$123.64	$123.65	$123.60
Purchase #3	$26.90	10.790%	$29.8025	$29.80	$29.80	$29.80
Purchase #4	$110.57	4.337%	$115.3654	$115.37	$115.35	$115.40
Purchase #5	$104.83	6.398%	$111.537	$111.54	$111.55	$111.50
Purchase #6	$217.64	10.723%	$240.9775	$240.98	$241.00	$241.00
Purchase #7	$109.76	7.337%	$117.8131	$117.81	$117.80	$117.80
7 purchase totals =	$781.14		$851.5986	$851.61	$851.60	$851.60