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	$138.78	8.499%	$150.5749	$150.57	$150.55	$150.60
Purchase #2	$236.60	5.710%	$250.1099	$250.11	$250.10	$250.10
Purchase #3	$70.55	10.563%	$78.0022	$78.00	$78.00	$78.00
Purchase #4	$45.26	9.378%	$49.5045	$49.50	$49.50	$49.50
Purchase #5	$36.49	9.275%	$39.8744	$39.87	$39.85	$39.90
Purchase #6	$131.87	8.221%	$142.711	$142.71	$142.70	$142.70
Purchase #7	$29.75	6.401%	$31.6543	$31.65	$31.65	$31.70
7 purchase totals =	$689.30		$742.4312	$742.41	$742.35	$742.50