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	$96.83	8.847%	$105.3966	$105.40	$105.40	$105.40
Purchase #2	$38.67	10.817%	$42.8529	$42.85	$42.85	$42.90
Purchase #3	$156.76	4.221%	$163.3768	$163.38	$163.40	$163.40
Purchase #4	$210.59	13.194%	$238.3752	$238.38	$238.40	$238.40
Purchase #5	$50.36	3.474%	$52.1095	$52.11	$52.10	$52.10
Purchase #6	$72.43	13.151%	$81.9553	$81.96	$81.95	$82.00
Purchase #7	$18.92	8.421%	$20.5133	$20.51	$20.50	$20.50
7 purchase totals =	$644.56		$704.5796	$704.59	$704.60	$704.70