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	$70.70	11.482%	$78.8178	$78.82	$78.80	$78.80
Purchase #2	$137.95	10.474%	$152.3989	$152.40	$152.40	$152.40
Purchase #3	$66.65	3.830%	$69.2027	$69.20	$69.20	$69.20
Purchase #4	$100.63	13.837%	$114.5542	$114.55	$114.55	$114.60
Purchase #5	$166.65	7.701%	$179.4837	$179.48	$179.50	$179.50
Purchase #6	$167.25	3.688%	$173.4182	$173.42	$173.40	$173.40
Purchase #7	$80.40	13.205%	$91.0168	$91.02	$91.00	$91.00
7 purchase totals =	$790.23		$858.8923	$858.89	$858.85	$858.90