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	$89.70	9.232%	$97.9811	$97.98	$98.00	$98.00
Purchase #2	$80.54	9.823%	$88.4514	$88.45	$88.45	$88.50
Purchase #3	$80.69	7.250%	$86.54	$86.54	$86.55	$86.50
Purchase #4	$200.93	3.791%	$208.5473	$208.55	$208.55	$208.50
Purchase #5	$85.65	4.860%	$89.8126	$89.81	$89.80	$89.80
Purchase #6	$137.41	7.603%	$147.8573	$147.86	$147.85	$147.90
Purchase #7	$134.27	9.786%	$147.4097	$147.41	$147.40	$147.40
7 purchase totals =	$809.19		$866.5994	$866.60	$866.60	$866.60