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	$201.54	9.698%	$221.0853	$221.09	$221.10	$221.10
Purchase #2	$237.79	10.541%	$262.8554	$262.86	$262.85	$262.90
Purchase #3	$89.62	12.608%	$100.9193	$100.92	$100.90	$100.90
Purchase #4	$188.64	9.606%	$206.7608	$206.76	$206.75	$206.80
Purchase #5	$80.86	11.476%	$90.1395	$90.14	$90.15	$90.10
Purchase #6	$27.59	3.816%	$28.6428	$28.64	$28.65	$28.60
Purchase #7	$171.70	4.208%	$178.9251	$178.93	$178.95	$178.90
7 purchase totals =	$997.74		$1,089.3282	$1,089.34	$1,089.35	$1,089.30