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	$79.65	12.761%	$89.8141	$89.81	$89.80	$89.80
Purchase #2	$131.32	9.389%	$143.6496	$143.65	$143.65	$143.60
Purchase #3	$164.92	12.872%	$186.1485	$186.15	$186.15	$186.10
Purchase #4	$99.89	4.592%	$104.4769	$104.48	$104.50	$104.50
Purchase #5	$127.39	7.446%	$136.8755	$136.88	$136.90	$136.90
Purchase #6	$112.29	12.373%	$126.1836	$126.18	$126.20	$126.20
Purchase #7	$78.88	3.354%	$81.5256	$81.53	$81.55	$81.50
7 purchase totals =	$794.34		$868.6738	$868.68	$868.75	$868.60