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	$136.78	3.630%	$141.7451	$141.75	$141.75	$141.70
Purchase #2	$96.56	6.563%	$102.8972	$102.90	$102.90	$102.90
Purchase #3	$167.79	11.628%	$187.3006	$187.30	$187.30	$187.30
Purchase #4	$11.40	9.557%	$12.4895	$12.49	$12.50	$12.50
Purchase #5	$10.67	4.106%	$11.1081	$11.11	$11.10	$11.10
Purchase #6	$134.27	13.238%	$152.0447	$152.04	$152.05	$152.00
Purchase #7	$160.54	3.327%	$165.8812	$165.88	$165.90	$165.90
7 purchase totals =	$718.01		$773.4664	$773.47	$773.50	$773.40