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	$236.94	13.325%	$268.5123	$268.51	$268.50	$268.50
Purchase #2	$12.46	8.136%	$13.4737	$13.47	$13.45	$13.50
Purchase #3	$120.90	5.620%	$127.6946	$127.69	$127.70	$127.70
Purchase #4	$138.49	4.850%	$145.2068	$145.21	$145.20	$145.20
Purchase #5	$250.66	13.512%	$284.5292	$284.53	$284.55	$284.50
Purchase #6	$242.67	11.807%	$271.322	$271.32	$271.30	$271.30
Purchase #7	$240.25	12.257%	$269.6974	$269.70	$269.70	$269.70
7 purchase totals =	$1,242.37		$1,380.4360	$1,380.43	$1,380.40	$1,380.40