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	$215.83	4.124%	$224.7308	$224.73	$224.75	$224.70
Purchase #2	$31.49	5.505%	$33.2235	$33.22	$33.20	$33.20
Purchase #3	$47.94	9.423%	$52.4574	$52.46	$52.45	$52.50
Purchase #4	$180.35	6.140%	$191.4235	$191.42	$191.40	$191.40
Purchase #5	$190.93	13.619%	$216.9328	$216.93	$216.95	$216.90
Purchase #6	$92.51	7.820%	$99.7443	$99.74	$99.75	$99.70
Purchase #7	$56.59	6.853%	$60.4681	$60.47	$60.45	$60.50
7 purchase totals =	$815.64		$878.9804	$878.97	$878.95	$878.90