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	$129.80	9.517%	$142.1531	$142.15	$142.15	$142.20
Purchase #2	$25.44	13.281%	$28.8187	$28.82	$28.80	$28.80
Purchase #3	$173.73	8.258%	$188.0766	$188.08	$188.10	$188.10
Purchase #4	$127.78	5.412%	$134.6955	$134.70	$134.70	$134.70
Purchase #5	$98.95	10.180%	$109.0231	$109.02	$109.00	$109.00
Purchase #6	$160.88	3.398%	$166.3467	$166.35	$166.35	$166.30
Purchase #7	$89.25	11.479%	$99.495	$99.50	$99.50	$99.50
7 purchase totals =	$805.83		$868.6087	$868.62	$868.60	$868.60