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	$103.87	4.689%	$108.7405	$108.74	$108.75	$108.70
Purchase #2	$8.31	7.362%	$8.9218	$8.92	$8.90	$8.90
Purchase #3	$118.60	11.106%	$131.7717	$131.77	$131.75	$131.80
Purchase #4	$98.89	13.310%	$112.0523	$112.05	$112.05	$112.10
Purchase #5	$63.40	12.111%	$71.0784	$71.08	$71.10	$71.10
Purchase #6	$239.88	9.719%	$263.1939	$263.19	$263.20	$263.20
Purchase #7	$139.28	3.486%	$144.1353	$144.14	$144.15	$144.10
7 purchase totals =	$772.23		$839.8939	$839.89	$839.90	$839.90