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	$100.72	10.185%	$110.9783	$110.98	$111.00	$111.00
Purchase #2	$241.39	12.416%	$271.361	$271.36	$271.35	$271.40
Purchase #3	$120.26	13.506%	$136.5023	$136.50	$136.50	$136.50
Purchase #4	$80.35	4.402%	$83.887	$83.89	$83.90	$83.90
Purchase #5	$107.82	3.702%	$111.8115	$111.81	$111.80	$111.80
Purchase #6	$19.63	5.347%	$20.6796	$20.68	$20.70	$20.70
Purchase #7	$87.41	13.334%	$99.0652	$99.07	$99.05	$99.10
7 purchase totals =	$757.58		$834.2849	$834.29	$834.30	$834.40