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	$50.91	6.617%	$54.2787	$54.28	$54.30	$54.30
Purchase #2	$156.59	9.390%	$171.2938	$171.29	$171.30	$171.30
Purchase #3	$97.42	5.271%	$102.555	$102.56	$102.55	$102.60
Purchase #4	$228.44	11.407%	$254.4982	$254.50	$254.50	$254.50
Purchase #5	$47.66	3.765%	$49.4544	$49.45	$49.45	$49.50
Purchase #6	$96.84	8.601%	$105.1692	$105.17	$105.15	$105.20
Purchase #7	$189.94	3.543%	$196.6696	$196.67	$196.65	$196.70
7 purchase totals =	$867.80		$933.9189	$933.92	$933.90	$934.10