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	$91.55	9.860%	$100.5768	$100.58	$100.60	$100.60
Purchase #2	$157.80	5.778%	$166.9177	$166.92	$166.90	$166.90
Purchase #3	$186.29	7.809%	$200.8374	$200.84	$200.85	$200.80
Purchase #4	$103.50	8.537%	$112.3358	$112.34	$112.35	$112.30
Purchase #5	$62.54	11.872%	$69.9647	$69.96	$69.95	$70.00
Purchase #6	$68.96	13.154%	$78.031	$78.03	$78.05	$78.00
Purchase #7	$67.97	5.305%	$71.5758	$71.58	$71.60	$71.60
7 purchase totals =	$738.61		$800.2392	$800.25	$800.30	$800.20