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	$97.39	12.122%	$109.1956	$109.20	$109.20	$109.20
Purchase #2	$76.40	5.301%	$80.45	$80.45	$80.45	$80.50
Purchase #3	$223.43	4.705%	$233.9424	$233.94	$233.95	$233.90
Purchase #4	$105.86	11.306%	$117.8285	$117.83	$117.85	$117.80
Purchase #5	$234.63	8.400%	$254.3389	$254.34	$254.35	$254.30
Purchase #6	$128.26	11.699%	$143.2651	$143.27	$143.25	$143.30
Purchase #7	$55.60	13.315%	$63.0031	$63.00	$63.00	$63.00
7 purchase totals =	$921.57		$1,002.0236	$1,002.03	$1,002.05	$1,002.00