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	$26.78	3.805%	$27.799	$27.80	$27.80	$27.80
Purchase #2	$82.69	7.810%	$89.1481	$89.15	$89.15	$89.10
Purchase #3	$103.94	9.299%	$113.6054	$113.61	$113.60	$113.60
Purchase #4	$19.94	3.416%	$20.6212	$20.62	$20.60	$20.60
Purchase #5	$55.56	13.624%	$63.1295	$63.13	$63.15	$63.10
Purchase #6	$147.36	10.238%	$162.4467	$162.45	$162.45	$162.40
Purchase #7	$162.70	13.453%	$184.588	$184.59	$184.60	$184.60
7 purchase totals =	$598.97		$661.3379	$661.35	$661.35	$661.20