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	$156.72	4.814%	$164.2645	$164.26	$164.25	$164.30
Purchase #2	$53.44	10.571%	$59.0891	$59.09	$59.10	$59.10
Purchase #3	$68.67	5.736%	$72.6089	$72.61	$72.60	$72.60
Purchase #4	$186.40	13.189%	$210.9843	$210.98	$211.00	$211.00
Purchase #5	$42.60	8.347%	$46.1558	$46.16	$46.15	$46.20
Purchase #6	$5.84	5.815%	$6.1796	$6.18	$6.20	$6.20
Purchase #7	$52.81	7.206%	$56.6155	$56.62	$56.60	$56.60
7 purchase totals =	$566.48		$615.8977	$615.90	$615.90	$616.00