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	$198.77	12.141%	$222.9027	$222.90	$222.90	$222.90
Purchase #2	$25.78	6.110%	$27.3552	$27.36	$27.35	$27.40
Purchase #3	$100.37	8.102%	$108.502	$108.50	$108.50	$108.50
Purchase #4	$234.67	8.291%	$254.1265	$254.13	$254.15	$254.10
Purchase #5	$114.98	11.189%	$127.8451	$127.85	$127.85	$127.80
Purchase #6	$101.63	10.460%	$112.2605	$112.26	$112.25	$112.30
Purchase #7	$165.87	9.794%	$182.1153	$182.12	$182.10	$182.10
7 purchase totals =	$942.07		$1,035.1073	$1,035.12	$1,035.10	$1,035.10