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	$142.96	3.793%	$148.3825	$148.38	$148.40	$148.40
Purchase #2	$52.38	5.223%	$55.1158	$55.12	$55.10	$55.10
Purchase #3	$122.28	4.551%	$127.845	$127.85	$127.85	$127.80
Purchase #4	$127.49	9.780%	$139.9585	$139.96	$139.95	$140.00
Purchase #5	$129.67	9.677%	$142.2182	$142.22	$142.20	$142.20
Purchase #6	$174.42	3.351%	$180.2648	$180.26	$180.25	$180.30
Purchase #7	$55.54	13.847%	$63.2306	$63.23	$63.25	$63.20
7 purchase totals =	$804.74		$857.0154	$857.02	$857.00	$857.00