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	$170.88	11.127%	$189.8938	$189.89	$189.90	$189.90
Purchase #2	$227.94	13.258%	$258.1603	$258.16	$258.15	$258.20
Purchase #3	$211.31	8.364%	$228.984	$228.98	$229.00	$229.00
Purchase #4	$19.25	3.321%	$19.8893	$19.89	$19.90	$19.90
Purchase #5	$212.32	13.566%	$241.1233	$241.12	$241.10	$241.10
Purchase #6	$127.30	11.625%	$142.0986	$142.10	$142.10	$142.10
Purchase #7	$88.38	7.395%	$94.9157	$94.92	$94.90	$94.90
7 purchase totals =	$1,057.38		$1,175.0650	$1,175.06	$1,175.05	$1,175.10