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	$89.38	10.447%	$98.7175	$98.72	$98.70	$98.70
Purchase #2	$81.75	7.308%	$87.7243	$87.72	$87.70	$87.70
Purchase #3	$72.95	12.155%	$81.8171	$81.82	$81.80	$81.80
Purchase #4	$220.81	8.563%	$239.718	$239.72	$239.70	$239.70
Purchase #5	$196.25	5.257%	$206.5669	$206.57	$206.55	$206.60
Purchase #6	$101.78	9.201%	$111.1448	$111.14	$111.15	$111.10
Purchase #7	$43.43	4.416%	$45.3479	$45.35	$45.35	$45.30
7 purchase totals =	$806.35		$871.0365	$871.04	$870.95	$870.90