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	$240.76	6.461%	$256.3155	$256.32	$256.30	$256.30
Purchase #2	$151.82	8.188%	$164.251	$164.25	$164.25	$164.30
Purchase #3	$148.61	5.638%	$156.9886	$156.99	$157.00	$157.00
Purchase #4	$98.68	3.670%	$102.3016	$102.30	$102.30	$102.30
Purchase #5	$132.61	8.836%	$144.3274	$144.33	$144.35	$144.30
Purchase #6	$127.73	11.479%	$142.3921	$142.39	$142.40	$142.40
Purchase #7	$175.44	11.105%	$194.9226	$194.92	$194.90	$194.90
7 purchase totals =	$1,075.65		$1,161.4988	$1,161.50	$1,161.50	$1,161.50