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	$31.47	8.394%	$34.1116	$34.11	$34.10	$34.10
Purchase #2	$91.44	5.345%	$96.3275	$96.33	$96.35	$96.30
Purchase #3	$112.28	13.264%	$127.1728	$127.17	$127.15	$127.20
Purchase #4	$40.84	6.136%	$43.3459	$43.35	$43.35	$43.30
Purchase #5	$102.97	6.781%	$109.9524	$109.95	$109.95	$110.00
Purchase #6	$112.65	12.772%	$127.0377	$127.04	$127.05	$127.00
Purchase #7	$10.45	7.196%	$11.202	$11.20	$11.20	$11.20
7 purchase totals =	$502.10		$549.1499	$549.15	$549.15	$549.10