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	$243.37	10.756%	$269.5469	$269.55	$269.55	$269.50
Purchase #2	$171.78	8.233%	$185.9226	$185.92	$185.90	$185.90
Purchase #3	$112.40	3.592%	$116.4374	$116.44	$116.45	$116.40
Purchase #4	$210.31	4.558%	$219.8959	$219.90	$219.90	$219.90
Purchase #5	$127.85	5.676%	$135.1068	$135.11	$135.10	$135.10
Purchase #6	$155.42	3.283%	$160.5224	$160.52	$160.50	$160.50
Purchase #7	$57.68	8.718%	$62.7085	$62.71	$62.70	$62.70
7 purchase totals =	$1,078.81		$1,150.1405	$1,150.15	$1,150.10	$1,150.00