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	$8.39	6.868%	$8.9662	$8.97	$8.95	$9.00
Purchase #2	$33.75	11.634%	$37.6765	$37.68	$37.70	$37.70
Purchase #3	$18.81	5.658%	$19.8743	$19.87	$19.85	$19.90
Purchase #4	$73.54	12.247%	$82.5464	$82.55	$82.55	$82.50
Purchase #5	$146.52	8.123%	$158.4218	$158.42	$158.40	$158.40
Purchase #6	$90.88	10.372%	$100.3061	$100.31	$100.30	$100.30
Purchase #7	$86.91	8.681%	$94.4547	$94.45	$94.45	$94.50
7 purchase totals =	$458.80		$502.2460	$502.25	$502.20	$502.30