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	$52.58	5.753%	$55.6049	$55.60	$55.60	$55.60
Purchase #2	$170.91	8.424%	$185.3075	$185.31	$185.30	$185.30
Purchase #3	$91.52	5.507%	$96.56	$96.56	$96.55	$96.60
Purchase #4	$29.30	12.628%	$33	$33.00	$33.00	$33.00
Purchase #5	$62.43	10.397%	$68.9208	$68.92	$68.90	$68.90
Purchase #6	$94.74	5.770%	$100.2065	$100.21	$100.20	$100.20
Purchase #7	$10.69	7.117%	$11.4508	$11.45	$11.45	$11.50
7 purchase totals =	$512.17		$551.0505	$551.05	$551.00	$551.10