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	$150.89	9.693%	$165.5158	$165.52	$165.50	$165.50
Purchase #2	$121.65	8.330%	$131.7834	$131.78	$131.80	$131.80
Purchase #3	$55.85	7.216%	$59.8801	$59.88	$59.90	$59.90
Purchase #4	$16.98	3.707%	$17.6094	$17.61	$17.60	$17.60
Purchase #5	$247.72	9.124%	$270.322	$270.32	$270.30	$270.30
Purchase #6	$243.85	6.623%	$260.0002	$260.00	$260.00	$260.00
Purchase #7	$151.97	10.310%	$167.6381	$167.64	$167.65	$167.60
7 purchase totals =	$988.91		$1,072.7490	$1,072.75	$1,072.75	$1,072.70