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	$73.49	7.270%	$78.8327	$78.83	$78.85	$78.80
Purchase #2	$76.97	7.153%	$82.4757	$82.48	$82.50	$82.50
Purchase #3	$129.36	12.551%	$145.596	$145.60	$145.60	$145.60
Purchase #4	$89.73	8.773%	$97.602	$97.60	$97.60	$97.60
Purchase #5	$139.87	9.826%	$153.6136	$153.61	$153.60	$153.60
Purchase #6	$179.72	4.432%	$187.6852	$187.69	$187.70	$187.70
Purchase #7	$212.67	10.195%	$234.3517	$234.35	$234.35	$234.40
7 purchase totals =	$901.81		$980.1569	$980.16	$980.20	$980.20