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	$13.77	8.104%	$14.8859	$14.89	$14.90	$14.90
Purchase #2	$12.62	10.504%	$13.9456	$13.95	$13.95	$13.90
Purchase #3	$48.55	6.722%	$51.8135	$51.81	$51.80	$51.80
Purchase #4	$171.90	7.542%	$184.8647	$184.86	$184.85	$184.90
Purchase #5	$173.80	4.665%	$181.9078	$181.91	$181.90	$181.90
Purchase #6	$31.36	13.230%	$35.5089	$35.51	$35.50	$35.50
Purchase #7	$65.43	3.319%	$67.6016	$67.60	$67.60	$67.60
7 purchase totals =	$517.43		$550.5280	$550.53	$550.50	$550.50