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	$89.98	9.571%	$98.592	$98.59	$98.60	$98.60
Purchase #2	$225.96	3.353%	$233.5364	$233.54	$233.55	$233.50
Purchase #3	$90.31	9.800%	$99.1604	$99.16	$99.15	$99.20
Purchase #4	$14.98	3.342%	$15.4806	$15.48	$15.50	$15.50
Purchase #5	$167.80	6.301%	$178.3731	$178.37	$178.35	$178.40
Purchase #6	$202.73	8.200%	$219.3539	$219.35	$219.35	$219.40
Purchase #7	$238.49	6.333%	$253.5936	$253.59	$253.60	$253.60
7 purchase totals =	$1,030.25		$1,098.0900	$1,098.08	$1,098.10	$1,098.20