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	$38.60	12.125%	$43.2803	$43.28	$43.30	$43.30
Purchase #2	$63.92	11.148%	$71.0458	$71.05	$71.05	$71.00
Purchase #3	$38.42	12.478%	$43.214	$43.21	$43.20	$43.20
Purchase #4	$214.82	12.345%	$241.3395	$241.34	$241.35	$241.30
Purchase #5	$86.82	13.869%	$98.8611	$98.86	$98.85	$98.90
Purchase #6	$178.81	3.145%	$184.4336	$184.43	$184.45	$184.40
Purchase #7	$130.33	3.516%	$134.9124	$134.91	$134.90	$134.90
7 purchase totals =	$751.72		$817.0867	$817.08	$817.10	$817.00