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	$178.25	6.318%	$189.5118	$189.51	$189.50	$189.50
Purchase #2	$221.64	9.832%	$243.4316	$243.43	$243.45	$243.40
Purchase #3	$102.66	6.657%	$109.4941	$109.49	$109.50	$109.50
Purchase #4	$35.97	10.724%	$39.8274	$39.83	$39.85	$39.80
Purchase #5	$156.59	11.404%	$174.4475	$174.45	$174.45	$174.40
Purchase #6	$64.44	3.377%	$66.6161	$66.62	$66.60	$66.60
Purchase #7	$136.46	5.700%	$144.2382	$144.24	$144.25	$144.20
7 purchase totals =	$896.01		$967.5667	$967.57	$967.60	$967.40