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	$33.59	12.352%	$37.739	$37.74	$37.75	$37.70
Purchase #2	$108.29	8.711%	$117.7231	$117.72	$117.70	$117.70
Purchase #3	$141.80	7.473%	$152.3967	$152.40	$152.40	$152.40
Purchase #4	$98.95	4.351%	$103.2553	$103.26	$103.25	$103.30
Purchase #5	$81.74	9.333%	$89.3688	$89.37	$89.35	$89.40
Purchase #6	$5.51	5.640%	$5.8208	$5.82	$5.80	$5.80
Purchase #7	$142.35	13.540%	$161.6242	$161.62	$161.60	$161.60
7 purchase totals =	$612.23		$667.9279	$667.93	$667.85	$667.90