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	$52.48	4.592%	$54.8899	$54.89	$54.90	$54.90
Purchase #2	$29.85	4.501%	$31.1935	$31.19	$31.20	$31.20
Purchase #3	$178.33	12.360%	$200.3716	$200.37	$200.35	$200.40
Purchase #4	$87.32	4.248%	$91.0294	$91.03	$91.05	$91.00
Purchase #5	$81.72	8.474%	$88.645	$88.65	$88.65	$88.60
Purchase #6	$103.45	7.461%	$111.1684	$111.17	$111.15	$111.20
Purchase #7	$222.98	10.854%	$247.1822	$247.18	$247.20	$247.20
7 purchase totals =	$756.13		$824.4800	$824.48	$824.50	$824.50