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	$227.55	4.290%	$237.3119	$237.31	$237.30	$237.30
Purchase #2	$128.74	4.761%	$134.8693	$134.87	$134.85	$134.90
Purchase #3	$36.30	3.487%	$37.5658	$37.57	$37.55	$37.60
Purchase #4	$113.71	7.765%	$122.5396	$122.54	$122.55	$122.50
Purchase #5	$115.65	10.572%	$127.8765	$127.88	$127.90	$127.90
Purchase #6	$90.94	13.290%	$103.0259	$103.03	$103.05	$103.00
Purchase #7	$136.44	5.627%	$144.1175	$144.12	$144.10	$144.10
7 purchase totals =	$849.33		$907.3065	$907.32	$907.30	$907.30