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	$66.90	9.465%	$73.2321	$73.23	$73.25	$73.20
Purchase #2	$58.90	9.671%	$64.5962	$64.60	$64.60	$64.60
Purchase #3	$218.32	10.628%	$241.523	$241.52	$241.50	$241.50
Purchase #4	$189.54	3.634%	$196.4279	$196.43	$196.45	$196.40
Purchase #5	$111.35	11.226%	$123.8502	$123.85	$123.85	$123.90
Purchase #6	$170.73	6.689%	$182.1501	$182.15	$182.15	$182.20
Purchase #7	$17.48	7.646%	$18.8165	$18.82	$18.80	$18.80
7 purchase totals =	$833.22		$900.5960	$900.60	$900.60	$900.60