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	$36.41	7.122%	$39.0031	$39.00	$39.00	$39.00
Purchase #2	$152.91	10.224%	$168.5435	$168.54	$168.55	$168.50
Purchase #3	$15.71	6.623%	$16.7505	$16.75	$16.75	$16.80
Purchase #4	$245.50	3.504%	$254.1023	$254.10	$254.10	$254.10
Purchase #5	$95.88	4.692%	$100.3787	$100.38	$100.40	$100.40
Purchase #6	$143.78	3.300%	$148.5247	$148.52	$148.50	$148.50
Purchase #7	$72.93	5.718%	$77.1001	$77.10	$77.10	$77.10
7 purchase totals =	$763.12		$804.4029	$804.39	$804.40	$804.40