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	$181.98	12.705%	$205.1006	$205.10	$205.10	$205.10
Purchase #2	$38.73	10.498%	$42.7959	$42.80	$42.80	$42.80
Purchase #3	$89.88	11.228%	$99.9717	$99.97	$99.95	$100.00
Purchase #4	$49.92	13.388%	$56.6033	$56.60	$56.60	$56.60
Purchase #5	$70.42	4.520%	$73.603	$73.60	$73.60	$73.60
Purchase #6	$41.77	8.623%	$45.3718	$45.37	$45.35	$45.40
Purchase #7	$134.79	9.180%	$147.1637	$147.16	$147.15	$147.20
7 purchase totals =	$607.49		$670.6100	$670.60	$670.55	$670.70