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	$165.59	8.834%	$180.2182	$180.22	$180.20	$180.20
Purchase #2	$116.45	6.723%	$124.2789	$124.28	$124.30	$124.30
Purchase #3	$33.53	11.200%	$37.2854	$37.29	$37.30	$37.30
Purchase #4	$21.71	7.356%	$23.307	$23.31	$23.30	$23.30
Purchase #5	$80.48	4.190%	$83.8521	$83.85	$83.85	$83.90
Purchase #6	$7.37	11.426%	$8.2121	$8.21	$8.20	$8.20
Purchase #7	$136.59	4.533%	$142.7816	$142.78	$142.80	$142.80
7 purchase totals =	$561.72		$599.9353	$599.94	$599.95	$600.00