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	$28.33	11.299%	$31.531	$31.53	$31.55	$31.50
Purchase #2	$225.25	7.227%	$241.5288	$241.53	$241.55	$241.50
Purchase #3	$97.39	4.400%	$101.6752	$101.68	$101.70	$101.70
Purchase #4	$9.71	9.708%	$10.6526	$10.65	$10.65	$10.70
Purchase #5	$44.97	12.401%	$50.5467	$50.55	$50.55	$50.50
Purchase #6	$19.33	9.815%	$21.2272	$21.23	$21.25	$21.20
Purchase #7	$67.47	7.261%	$72.369	$72.37	$72.35	$72.40
7 purchase totals =	$492.45		$529.5305	$529.54	$529.60	$529.50