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	$10.38	9.111%	$11.3257	$11.33	$11.35	$11.30
Purchase #2	$71.81	13.796%	$81.7169	$81.72	$81.70	$81.70
Purchase #3	$110.58	8.296%	$119.7537	$119.75	$119.75	$119.80
Purchase #4	$197.90	8.428%	$214.579	$214.58	$214.60	$214.60
Purchase #5	$90.28	10.230%	$99.5156	$99.52	$99.50	$99.50
Purchase #6	$85.89	7.824%	$92.61	$92.61	$92.60	$92.60
Purchase #7	$131.94	6.175%	$140.0873	$140.09	$140.10	$140.10
7 purchase totals =	$698.78		$759.5882	$759.60	$759.60	$759.60