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	$109.99	10.285%	$121.3025	$121.30	$121.30	$121.30
Purchase #2	$185.56	9.677%	$203.5166	$203.52	$203.50	$203.50
Purchase #3	$172.34	4.494%	$180.085	$180.09	$180.10	$180.10
Purchase #4	$51.51	5.346%	$54.2637	$54.26	$54.25	$54.30
Purchase #5	$98.50	11.549%	$109.8758	$109.88	$109.90	$109.90
Purchase #6	$16.76	12.521%	$18.8585	$18.86	$18.85	$18.90
Purchase #7	$18.72	11.294%	$20.8342	$20.83	$20.85	$20.80
7 purchase totals =	$653.38		$708.7363	$708.74	$708.75	$708.80