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	$233.94	11.145%	$260.0126	$260.01	$260.00	$260.00
Purchase #2	$142.71	12.124%	$160.0122	$160.01	$160.00	$160.00
Purchase #3	$18.62	7.560%	$20.0277	$20.03	$20.05	$20.00
Purchase #4	$113.71	11.786%	$127.1119	$127.11	$127.10	$127.10
Purchase #5	$57.43	7.130%	$61.5248	$61.52	$61.50	$61.50
Purchase #6	$40.85	12.189%	$45.8292	$45.83	$45.85	$45.80
Purchase #7	$7.42	7.860%	$8.0032	$8.00	$8.00	$8.00
7 purchase totals =	$614.68		$682.5216	$682.51	$682.50	$682.40