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	$9.82	11.182%	$10.9181	$10.92	$10.90	$10.90
Purchase #2	$82.64	7.650%	$88.962	$88.96	$88.95	$89.00
Purchase #3	$5.86	12.694%	$6.6039	$6.60	$6.60	$6.60
Purchase #4	$65.89	10.585%	$72.8645	$72.86	$72.85	$72.90
Purchase #5	$177.66	6.151%	$188.5879	$188.59	$188.60	$188.60
Purchase #6	$47.64	13.573%	$54.1062	$54.11	$54.10	$54.10
Purchase #7	$168.79	6.714%	$180.1226	$180.12	$180.10	$180.10
7 purchase totals =	$558.30		$602.1652	$602.16	$602.10	$602.20