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	$214.81	11.209%	$238.8881	$238.89	$238.90	$238.90
Purchase #2	$180.43	13.379%	$204.5697	$204.57	$204.55	$204.60
Purchase #3	$51.83	8.112%	$56.0344	$56.03	$56.05	$56.00
Purchase #4	$28.90	7.716%	$31.1299	$31.13	$31.15	$31.10
Purchase #5	$82.37	13.267%	$93.298	$93.30	$93.30	$93.30
Purchase #6	$53.32	3.379%	$55.1217	$55.12	$55.10	$55.10
Purchase #7	$198.37	6.530%	$211.3236	$211.32	$211.30	$211.30
7 purchase totals =	$810.03		$890.3654	$890.36	$890.35	$890.30