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	$150.86	13.544%	$171.2925	$171.29	$171.30	$171.30
Purchase #2	$174.60	11.710%	$195.0457	$195.05	$195.05	$195.00
Purchase #3	$65.40	5.852%	$69.2272	$69.23	$69.25	$69.20
Purchase #4	$105.29	5.150%	$110.7124	$110.71	$110.70	$110.70
Purchase #5	$239.42	4.365%	$249.8707	$249.87	$249.85	$249.90
Purchase #6	$82.57	8.177%	$89.3217	$89.32	$89.30	$89.30
Purchase #7	$191.98	12.246%	$215.4899	$215.49	$215.50	$215.50
7 purchase totals =	$1,010.12		$1,100.9601	$1,100.96	$1,100.95	$1,100.90