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	$170.54	10.158%	$187.8635	$187.86	$187.85	$187.90
Purchase #2	$135.78	7.709%	$146.2473	$146.25	$146.25	$146.20
Purchase #3	$73.92	12.417%	$83.0986	$83.10	$83.10	$83.10
Purchase #4	$80.62	4.841%	$84.5228	$84.52	$84.50	$84.50
Purchase #5	$97.80	5.613%	$103.2895	$103.29	$103.30	$103.30
Purchase #6	$231.53	9.511%	$253.5508	$253.55	$253.55	$253.60
Purchase #7	$116.35	12.843%	$131.2928	$131.29	$131.30	$131.30
7 purchase totals =	$906.54		$989.8653	$989.86	$989.85	$989.90